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B) Skeleton equation

i. Organic waste is decomposed by micro-organism and as a result manure and bio gas are formed.

ii. Alcohol is formed on mixing yeast in glucose solution under proper condition.

iii. The chemical reaction during which H_2(g) s lost is termed as oxidation.

iv. Corrosion can be prevented by using antirust solution.

v. The chemical reactions in which heat is liberated are called exothermic reactions.

C) Equal number of atoms of different elements on reactant side and product side

(1) In the reaction of dil. HCl and Shahabad tile, CO₂ effervescence is formed slowly. On the other hand, C₂ effervescence forms at faster speed with the powder of Shahabad tile.

(2) The above observation indicates that the rate of a reaction depends upon the size of the particles of the reactants taking part in the reaction. Smaller the size of the reactant particles taking part in a reaction faster will be the rate of reaètion.

The naturally occurring chemical substance in which metal occurs in the earth’s crust is called mineral. 

On the other hand, the mineral from which metal can be economically and conveniently extracted is called an ore.

It is not necessary that a new substance is always formed.

False

During endothermic reactions, heat is transferred from the surroundings to the reacting substances. On the other hand, heat is transferred from the reacting substances to the surroundings.

Hence, the given statement is false

True

The insoluble substance formed during a chemical reaction is known as a precipitate. The precipitate formed in a double displacement reaction.

Hence, the given statement is true.

In the process of dissolution, new substance is not necessarily formed. Whereas in a chemical reaction a new substance is definitely formed.

The aluminium utensils when kept in the house for a few days, oxidation of aluminium takes place, a thin laver aluminium oxide (Al₂O₃) is deposited on the surface. Hence, aluminium utensils lose their lustre in a few days.

s-Block elements:

• s-Block contains group 1 and group 2 elements.
• It contains only metals.
• The last electron in the s-block elements enters in s orbital.
• General outer electronic configuration of s-block elements is ns^1-2.
• e.g. Na, K, Ca, Mg, etc.

p-Block elements:

• p-Block contains elements from groups 13 to 18.
• It contains metals, nonmetals as well as metalloids.
• The last electron in the p-block elements enters in p orbital.
• General outer electronic configuration of p-block elements is ns² np^1-6.
• e.g. C, N, O, F, etc.

i. Lanthanide series: The fourteen elements after lanthanum (Z = 57) i.e., from cerium (Z = 58) to lutetium (Z = 71) are named after their preceding member (₅₇La) present in the third group and 6^th period and are called lanthanides. They are kept in separate series called lanthanide series at the bottom of the modem periodic table.

ii. Actinide series: The fourteen elements after actinium i.e., from thorium (Z = 90) to lawrencium (Z = 103) are named after ₈₉Ac present in third period and 7^th group. They are kept in separate series called actinide series at the bottom of the modem periodic table.

d-Block elements:

• d-Block contains elements from group 3 to group 12.
• It is present in the middle of the modern periodic table.
• They are also known as transition elements.
• The last electron in the d-block elements enters in d orbital.
• General outer electronic configuration of d-block elements is ns^0-2 (n-1)d^1-10.
• e.g. Cu, Zn, Cr, Ti, V, etc.

f-Block elements:

• f-Block contains elements of lanthanide and actinide series.
• f-block elements are present below the modern periodic table as two separate rows.
• They are also known as inner transition elements.
• The last electron in the f-block elements enters in f orbital.
• General outer electronic configuration of f-block elements is ns² (n-1) d^0-1 (n - 2) f¹¹⁴.
• e.g. Ce, Pr, Nd Th, U, Np, etc.

Dominance: It is a phenomenon in which when two contrasting alleles are present together, only one expresses itself and is called dominant whereas the other which does not express itself is called recessive. 

Co-dominance: It is a phenomenon in which when two contrasting alleles are present together, both of the alleles express themselves. 

Incomplete dominance: It is a phenomenon in which when two contrasting alleles are present together neither of the alleles is dominant over other and the phenotype formed is intermediate of the two alleles. . ., 

Red flower × White flower → Pink flower colour

Correct option is: (C) Group 16

Group 16 elements are known as chalcogens.

Correct option is (C) Group 16

• The chemical reactivity can be illustrated by comparing the reaction of elements with oxygen to form oxides and the nature of the oxides.
• Alkali metals present on the extreme left of the modem periodic table are highly reactive and thus, they react vigorously with oxygen to form oxides such as Na₂O which reacts with water to form strong bases like NaOH.
• The reactive elements on the right i.e., halogens react with oxygen to form oxides such as Cl₂O₇ which on reaction with water form strong acids like HClO₄.
• The oxides of the elements in the centre of the main group elements are either amphoteric (Al₂O₃) neutral (CO,NO) or weakly acidic (CO₂).

i. Valency of an element:

• Valency of an element indicates the number of chemical bonds that the atom can form giving a molecule.
• The most fundamental chemical property of an element is its combining power. This property is numerically expressed in terms of valency or valence.
• Valence does not have any sign associated with it.
• Valency of the main group elements is usually equal to the number of valence electrons (outer electrons) and/or equal to difference between 8 and the number of valence electrons.

ii. Oxidation state (or oxidation number):

• The oxidation state or oxidation number is a frequently used term related to valence.
• Oxidation number has a sign, + or – which is decided by the electronegativities of atoms that are bonded.

iii. Chemical reactivity:

• Chemical reactivity is related to the ease with which an element loses or gains the electrons.
• Chemical properties of elements depend on their electronic configuration.

Correct option is B) 2, 3

C) N₂ + O₂ → 2NO 

D) All are correct

• Electronic configuration of Al is [Ne] 3s² 3p¹,₁₄Si is [Ne] 3s² 3p² and that of ₁₅P is [Ne] 3s² 3p³.
• Metals are characterized by the ability to form compounds by loss of valence electrons.
• ‘Al’ has 3 valence electrons, thus shows tendency to lose 3 valence electrons to complete its octet. Hence, Al is a metal.
• Nonmetals are characterized by the ability to form compounds by gain of valence electrons in valence shell.
• ‘P’ has 5 valence electrons thus, shows tendency to gain 3 electrons to complete its octet. Hence, ‘P’ is a nonmetal.
• Si has four valence electrons, thus it can either lose/gain electrons to complete its octet. Hence, behaves as a metalloid.

i. Metals are present in all the four blocks of the periodic table.

ii. Salts of metals in the f-block and p-block (except AlCl₃) are not common laboratory chemicals. Therefore, the choice is between sand d-block.

iii. From the given properties their placement is done as shown below:

• s-block: Metal that reacts vigorously with water.
• d-block: Metal that reacts slowly with water.

iv. The colourless nature of the less reactive metal in the d-block implies that the inner d subshell is completely filled.

A. Ge (belongs to period 4 and group 14) :

a. Ge belongs to period 4.

Therefore, 

n = 4.

b. Group 14 indicates that the element belongs to the p-block of the modem periodic table.

c. The general outer electronic configuration of group 14 elements is ns² np². 

d. Thus, the outer electronic configuration of Ge is 4s² 4p².

B. Po (belongs to period 6 and group 16) :

a. Po belongs to period 6. 

Therefore,

n = 6.

b. Group 16 indicates that the element belongs to the p-block of the modem periodic table.

c. The general outer electronic configuration of group 16 elements is ns² np⁴.

d. Thus, the outer electronic configuration of Po is 6s² 6p⁴.

C. Cu (belongs to period 4 and group 11) :

a. Cu belongs to period 4. 

Therefore, 

n = 4.

b. Group 11 indicates that the element belongs to the d-block of the modem periodic table.

c. The general outer electronic configuration of the d-block elements is ns^0-2 (n-1)d^1-10.

d. The expected configuration of Cu is 4s² 3d⁹. 

However, 

The observed configuration of Cu is 4s¹ 3d¹⁰. 

This is due to the extra stability associated with completely filled d-subshell. 

Thus, 

The outer electronic configuration of Cu is 4s¹ 3d¹⁰.

• Electronic configuration of ₂₉CU is [Ar] 3d¹⁰ 4s². while that of Zn is [Ar] 3d¹⁰4s².
• Electronic configuration of Cu in its +1 oxidation state is [Ar] 3d¹⁰ while that in +2 oxidation state is [Ar] 3d⁹.
• Therefore, Cu contains partially filled d orbitals in +2 oxidation state and thus, Cu²⁺ salts are coloured.
• However, Zn has completely filled d orbital which is highly stable and hence, it does not form coloured ions.

Hence, 

Cu forms coloured salts while Zn forms colourless salts.

The modem periodic table is divided into four blocks based on the subshell in which the last electron enters.

• A period begins by filling of one electron to the ‘s’ subshell of a new shell and ends when an element corresponding to the same shell attains complete octet (or duplet).
• Between these two ‘s’ and ‘p’ subshell of the valence shell, the inner subshells ‘d’ and ‘f’ are filled successively following the aufbau principle.

The general outer electronic configuration of s-block elements is ns^1-2.

The general electronic configuration for the p-block elements is ns²np^1-6.

• The subshell in which the last electron enters decides the block to which an element belongs.
• In group 1 and group 2 elements, the last electron is filled in the s subshell.

Therefore, the elements of group 1 and group 2 are known as s-block elements.

• Electronic configuration of helium is 1s² which indicates that it has a stable electronic configuration i.e., a complete duplet.
• The p-block ends with group 18 which is a family of inert gases having stable electronic configuration (complete octet except helium).
• Therefore, helium is placed with group 18 elements in p-block due to its stable electronic configuration even though its last electron enters in s subshell.

• The elements present in f-block are all metals and are placed in the two rows called lanthanide series (₅₈Ce to 71Lu) and actinide series (₉₀Th to ₁₀₃Lr).
• The lanthanides are also known as rare earth elements while the actinide elements beyond ₉₂U are called transuranium elements.
• All the transuranium elements are manmade and radioactive.
• The last electron of the elements of these series is filled in the (n-2)f subshell, and therefore, these are called inner transition elements.
• These elements have very similar properties within each series.

• The 6^th period begins by filling the last electron in the subshell ‘6s’ and ends by completing the subshell ‘6p’. Therefore, the sixth period has the subshells filled in increasing order of energy as 6s < 4f < 5d < 6p.
• The electron capacities of these subshells are 2, 14, 10 and 6, respectively. Therefore, the total number of elements in the 6^th period is 2 + 14 + 10 + 6 = 32.

• The d-block contains elements of the groups 3 to 12 which are all metals. They are also known as transition elements or transition metals.
• They form a bridge between chemically reactive s-block elements and less reactive elements of groups 13 and 14.
• Most of the d-block elements possess partially filled inner d orbitals. As a result, the d-block elements have properties such as variable oxidation state, paramagnetism, ability to form coloured ions. They can be used as catalysts.
• Zn, Cd, and Hg with configuration ns² (n-1)d¹⁰, (completely filled s and d subshells) do not show characteristic properties of transition metals as they are stable.

The fifth period accommodates 18 elements as a result of successive filling of electrons in the 5s, 4d and 5p subshells.

The 6^th period begins by filling the last electron in the shell with n = 6. The lowest energy subshell of any shell is ‘s’. 

Therefore, the last electron of the first element in the 6^th period enters the subshell ‘6s’.

The p-block elements together with s-block elements are called main group elements or representative elements.

A d subshell is present in the shells with n ≥ 3 and according to the (n+1) rule, the energy of ns orbital is less than that of the (n-1)d orbital. As a result, the last electron enters a (n-1)d orbital only after the ns subshell is completely filled.

Correct option is: (C) P < Si < Ai < Na

As we move along a period from left to right the radii of element decrease. Na, Si, Al and P are third period elements 

Therefore, the order of radii is Na > Al > Si > P

(C) P < Si < Al < Na

• The s-block contains the elements of group 1 (alkali metals) and group 2 (alkaline earth metals).
• They occur in nature only in combined state as they are reactive elements.
• Except Li and Be, compounds formed by all other s-block elements are predominantly ionic in nature.
• This is because they have only one or two valence electrons which they can lose readily forming M⁺ or M²⁺ ions.
• Since they can lose electrons easily, they have low ionization enthalpies, which decreases down the group resulting in increased reactivity.

• Chemical properties of elements depend upon their valency.
• Elements belonging to the same group have the same valency.

Hence,

The elements belonging to the same group show similar chemical properties.

i. Mg (Z = 12): Atomic number of Mg is 12. 

Electronic configuration is 1s² 2s² 2p⁶ 3s².

Block: Since the last electron enters s subshell (3 s), Mg belongs to s-block.

Period: n = 3. Therefore, it is present in the third period.

Group: For s-block element, group number = number of valence electrons = 2. Hence, it belongs to group 2.

ii. V (Z = 23): Atomic number of V is 23.

Electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s².

Block: Since the last electron enters d subshell (3d), V belongs to d-block.

Period: n = 4. Therefore, it is present in the fourth period.

Group: For d-block elements, group number = 2 + number of (n – 1)

d electrons = 2 + 3 = 5. 

Hence, it belongs to group 5.

iii. Sb (Z = 51): Atomic number of Sb is 51.

Electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p³.

Block: Since the last electron enters p subshell (5p), Sb belongs to p-block.

Period: n = 5. Therefore, it is present in the fifth period.

Group: For p block elements, group number = 18 – number of electrons required to complete octet = 18 – 3 = 15. 

Hence, it belongs to group 15.

iv. Rn (Z = 86): Atomic number of Rn is 86.

Electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶.

Block: Since the last electron enters p subshell (6p), Rn belongs to p-block.

Period: n = 6. Therefore, it is present in the sixth period.

Group: For p block elements, group number = 18 – number of electrons required to complete octet = 18 – 0 = 18. 

Hence, it belongs to group 18.

v. Na (Z = 11): Atomic number of Na is 11.

Electronic configuration is 1s² 2s² 2p⁶ 3s¹.

Block: Since the last electron enters s subshell (3s), Na belongs to s-block.

Period: n = 3. Therefore, it is present in the third period.

Group: For s-block element, number of the group = number of valence electrons = 1.

Hence, it belongs to group 1.

vi. Cl (Z = 17): Atomic number of Cl is 17.

Electronic configuration is 1s² 2s² 2p⁶ 3s² 3p⁵.

Block: Since the last electron enters p subshell (3p), Cl belongs to p-block.

Period: n = 3. Therefore, it is present in the third period.

Group: For p block elements, group number = 18 – number of electrons required to complete octet = 18 – 1 = 17.

Hence, it belongs to group 17.

Following are some other examples of periodic events :

• Motion of earth around the sun. 
• Rotation of earth around its own axis. 
• Day and night.

The distribution of electrons in an atom is according to the following three principles :

1. Aufbau principle 

2. Pauli’s exclusion principle 

3. Hund’s rule of maximum multiplicity

[Note : According to aufbau principle, electrons are filled in the subshells in the increasing order of their energies which follows the following order : s < p < d < f.]

Correct option is: (D) 18, 18 and 32

First, second, third, fourth, fifth and sixth periods contain 2, 8, 8, 18, 18, 32 elements respectively. While seventh periods is incomplete

Hence, fourth, fifth and sixth period contain 18, 18, 32 element respectively.

(D) 18, 18 and 32

D) double displacement

(a) 2KClO₃ → 2KCl + O₂ 

(b) Zn + 2HCl → ZnCl₂ + H₂

(c) 2FeCl₂ + Cl₂ → 2FeCl₃

(d) 2CO + O₂ → 2CO₂

(e) 2Ca + O₂ → 2CaO 

(f) 4Na + O₂ → 2Na₂O 

(g) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O 

(h) 2AgBr → 2Ag + Br₂

(i) 2KNO₂ → 2KNO₂ + O₂

• Electrons present in the outermost shell of the atom of an element are called valence electrons.
• 3Li is an s-block element and its electronic configuration is 1s²2s¹. Since it has one valence electron, it is placed in group 1.
• Therefore, for s-block elements, group number = number of valence electrons.
• However, for p-block elements, group number = 18 – number of electrons required to attain complete octet.
• 7N is a p-block element and its electronic configuration is 1s²2s²2p³. Since it has five electrons in its valence shell, it is short of three electrons to complete its octet.
• Therefore, its group number = 18 – 3 = 15. 

Activity Series: The activity series of metals is a list of metals in the order of their decreasing chemical activity

• When two atoms of different elements form a covalent bond, the electron pair is shared unequally.
• Electronegativity represents attractive force exerted by the nucleus on shared electrons. Electron sharing between covalently bonded atoms takes place using the valence electron.
• It depends upon the effective nuclear charge experienced by electron involved in formation of the covalent bond.
• Electronegativity predicts the nature of the bond, or, how strong is the force of attraction that holds two atoms together.

Correct option is: (B) F^- < O^2- <N^3-

Isoelectronic species with more negative changes have large ionic radii than less negative. Therefore, the correct order of radii is \(N^{3^\circ} > O^{2^\circ} > F^-\)

(B) F^- < O^2- <N^3-

(D) 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³ 4s²