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Mg or Magnesium do not belongs to this triad

Mendeleeff’s periodic table is prepared based on atomic mass whereas modem periodic table is prepared based on atomic number (electronic configuration).

When electrically charged particles moves under acceleration, alternating electrical and magnetic fields are produced and transmitted. These fields are transmitted in the form of wave called electromagnetic waves or radiations.

Potassium is placed below sodium in group 1. It, therefore has one more electron shell. Na atom has three electron shells (2, 8,1); K atom has four (2, 8, 8,1). So, potassium atom is bigger than sodium atom.

Magnesium atom precedes calcium atom in the same group, i.e., group 2. Magnesium atom has got three electron shells (2, 8, 2) whereas calcium atom has four electron shells (2, 8, 8, 2). So, calcium atom is larger than the sodium atom.

Magnesium come after sodium in the same period. Atoms of both elements have three electron shells (Na : 2, 8, 1 : Mg : 2, 8, 2). But the nuclear charge of sodium is + 11 and that of magnesium is + 12. Hence, the electron shells are pulled inward more strongly in Mg atom than in Na atom. Hence, Mg atom is smaller than Na atom.

K⁺ is larger than Na⁺ because the ionic radius increases in a particular group on moving from top to bottom due to increase in the principle energy shell though the number or electrons in the valence shell remain the same. 

Mg²⁺ ion is smaller than O^2- ion though both are iso-electronic. The nuclear charge in Mg²⁺ is + 12 and O^2- is + 8, so with the increase in nuclear charge the size decreases and, hence O^2- > Mg²⁺.

 The electronic configuration of Li = 2, 1. 

The electronic configuration of Na = 2, 8, 1.

 The electronic configuration of K = 2, 8, 8, 1.

All the three have one electron in the outermost shell which they lose to form positively charged species, i.e., Li⁺ , Na⁺ and K⁺ .

When an atom loses an electron then the element is said to be a reducing agent. The reducing power of an element depends upon how quickly it can lose electrons. In case of electrons held very loosely by the nucleus such element can easily lose their valence electrons and hence, higher reducing agent.

Na, Mg, Al, Si, P, S, Cl, Ar all elements present in third short period in Periodic Table. These elements are known as typical elements. Francium, Mercury and Bromine are known as liquid elements.

(i) Hydrogen is placed in IA group. 

(ii) The horizontal rows in Periodic Table are known as periods. There are seven periods in all. 

(iii) There are only two elements in the first period. 

(iv) The second and third periods have eight elements each. 

(i) There are seven periods in Periodic Table. 

(ii) There are nine groups, numbered from 0 to 8. 

(iii) The groups IA, IIA, IIIA. IVA, VA, VIA and VILA consist normal elements and groups, IIIB, IVB, VB, VIB, VIIB and IB, IIB consist transition elements. 

(iv) Zero group (Noble gases). 

(v) The first column is numbered zero, whereas last group is numbered 8.

 The reducing power of an element depends upon, how quickly it can lose electrons in the valence shell. As one moves from left to right in Periodic Table, the electrons in valence shell are held more tightly because of increase of nuclear charge. Thus, the tendency of atoms to lose their electrons gradually decreases and so does the reducing power. 

(i) The atoms of the elements at the end of period 2 and Period 3 contains 8 electrons in their outermost shell. 

(ii) Non-metallic. 

(iii) Metallic. 

 The atomic size of elements decreases on moving from left to right in Period. 

(i) J 

(ii) R 

(iii) M 

(iv) Five 

(v) T 

(vi) y-Krypton 

(vii) Ionic bond. Molecular formula ⟶ A₂H

(i) Arrangement of elements in the III rd group of Periodic Table is given below : Na, Mg, Al, Si, P, S, Cl. 

(ii) Lower, Higher.

B) a – iii, b – i, c – ii

(i) P is a noble gas with atomic number 18, i.e., 2, 8, 8. H is a also a noble gas with atomic number 10, i.e. 2, 8. 

(ii) G is halogen with atomic number 9, i.e. 2, 7. O is also a halogen with atomic number 17, i.e. 2,8, 7. 

(iii) A and I are alkali metals. 

(iv) D and L are elements with valency 4.

B) atomic weight

(i) T, 

(ii) G, 

(iii) G and S, 

(iv) H and P, 

(v) D and L, 

(vi) Q, 

(vii) E, 

(viii) The halogens, 

(ix) I : Sodium, J : Magnesium; N: Phosphorus; O: Chlorine.

 These are: 

(i) Magnitude of nuclear charge 

(ii) Number of shells 

(iii) Screening or shielding effect

(i) Oxygen and sulphur 

(ii) Chromium 

(iii) Calcium 

(iv) Sulphur 

(v) Calcium 

(vi) Calcium 

(vii) Chromium 

(viii) Silicon 

(ix) Helium and Krypton 

(x) Chromic acid produced by chromium. 

Ionisation energy of O is less than that of N because it is very easy to remove electrons from oxygen than from nitrogen. Hence, ionisation energy of O is less than that of N.

 X – 1.33 Å; Y – 0.95 Å; Z – 0.60 Å. 

The order of increasing atomic numbers is : Z < Y < X. This order is due to the fact, that greater is the ionic radii, greater is the atomic number of the element. As the ionic radii increases, the number of electrons increases, i.e., the atomic number increases.

Energy of one photon

E = hv = hc/λ = {6.626 x 10^-34 Js x 3 x 10⁸ ms^-1}/{337.1 x 10^-9 m}

= 5.89 x 10^-19 J

Power of the laser = 5.89 x 10^-19 J x 5.6 x 10²⁴

= 32.98 x 10⁵ Js^-1

= 32.98 x 10⁵ Watt

(i) Cu = 1.22Å; Cu⁺ = 0.96Å; Cu²⁺ = 0.72Å. 

(ii) Mg²⁺ (0.65Å) is smaller than Na+ (0.96Å) because as the effective nuclear charge per electron increases, the electrons are more strongly attracted and pulled towards the nucleus which causes a decrease in size of the Mg²⁺ ion.

Eka-Aluminium and Eka-Silicon are known as Gallium and Germanium respectively.

Halogen.

The elements of group 17 are collectively called as Halogen.

The chemical and physical properties of the elements are periodic functions of their atomic masses.

Correct Option is : (B) The mass of electron is equal to the mass of neutron.

Electrons is a negatively charge particle , it is a basic constiuent of atoms at is a also constitunet of cathode ray. The mass of electron is approx \(\frac{1}{1837}\) times of the mass of proton and neutrons.

Option : (B) The mass of electron is equal to the mass of neutron.

Fluorine, Chlorine, Bromine, Iodine, and Astatine of VIIA group elements are called halogens, which are obtained from sea salt.

In group 17, 2^nd row, element 'A' is F 

In group 16, 2^nd row, element 'B' is O 

In group 15, 2^nd row, element 'C' is N 

Decreasing order of electronegativity 

(EN) = F > O > N 

Decreasing order of ionization energy 

(IE) = F > N > O 

Decreasing order of electron gain enthalpy 

(EGE) = F > O > N

Correct option is  C) VII A

The chemical properties of elements depend upon the number of electrons in the outermost shell of an atom, These electrons are called valence electrons and thus determines the valency of the atom (or element). in representative elements, the valency is generally equal to either n or (8 - n), where n is number of valence electrons in the atom. In a period, valence electrons increase from 0 to 8 on moving from left to right. The valency of an element w.r.t. H and Cl increases from 1 to 4 and then decreases to zero. However w.r.t. oxygen, valency increases from 1 to 7 and then becomes zero in noble gases. In a group, the number of valence electrons remains the same and therefore all elements in a group exhibit same valency, e.g., all elements of group 1 have valency one and those of group 2 have valency two. However, the transition elements exhibit variable valency.

Correct option is  D) All

A) s – block elements

(i) [Ar]4s² is Calcium metal with At. no. = 20.

(ii) [Ar] 3d¹⁰4s² is Zinc metal with At. no. = 30.

(iii) [Ar] 3d¹⁰4s²4p¹5s⁶ is Strontium metal with At. no. = 38.

(iv) [Ar] 3d¹⁰4s²4p⁶5s² is Rubidium metal with At. no. = 37.

Alkali metals are most metallic, followed by alkaline earth metals and transition metals.

Among alkali metals - Rubidium (37) is most metallic. Among alkaline earth metals (Ca, Sr), Sr (Strontium) is more metallic than Calcium (Ca) as metallic character increases from top to bottom in a group. Zinc, the transition metal is least metallic. Thus, metallic character increases from

Zn < Ca < Sr < Rb or (ii) < (i) < (iii) < (iv)

(a) Increasing order of size F < CI < Br < I

(b) Increasing order of oxidizing powder, I < Br < Cl < F

(i) K is larger in size than K⁺ . The electronic configuration of K and K⁺ are:

K ∶ 1s² , 2s²2p⁶ ,3s²3p⁶ ,4s¹

K⁺ ∶ 1s² , 2s²2p⁶ , 3s²3p⁶,

K⁺ is formed from K when the later loses its 4 electrons.

K → K⁺ + e⁻

As seen from the electronic configurations of K and K⁺ , the K⁺ ion has 18 electrons and K atom has 19 electrons but the nuclear charge in both these species is the same (+ 19). Since K⁺ ion has 1 electron less than K atom, the forces of attraction between the nucleus and the electrons are more strong in K⁺ ion than in K atom. This results in more inward pulling of electrons towards the nucleus in K⁺ ion and hence its size decreases.

(ii) Bris formed by the gain of one electron by Br atom. In Br^- the nuclear charge is the same as that in the Br atom but the number of electrons has increased. Since same nuclear charge now acts on increased number of electrons, the effective nuclear charge per electron decreases in Br^-. The electron cloud is held less tightly by the nucleus. This causes increase in the size.

Halogen = Br

Metal = Hg

Group 13 element = Ga

B) decreases

Electronic configuration of ₄Ве = 2, 2 = 1s² , 2s²

Electronic configuration of ₅B = 2, 3 = 1s² , 2s² , 2p¹

In case of Be, more energy is required to remove an electron from 2s orbital as it is completely filled as compared to B. So, first I.E. of boron is less than Be. But size of Be is more than boron because atomic size decreases from left to right in a period due to increase in nuclear charge.

Correct option is  D) All

(a) C, (b) N, (c) Ne.

(a) O > F > N > C, second ionization potential of oxygen is highest since electron is to be removed from half filled configuration for rest follow the order of size.

(b) N > C > P > Si, nitrogen has smallest size and so has higher tendency to attract shared pair of electrons. 

(c) Si > Al > Mg > Na, silicon has highest first ionization potential due to smallest size, Mg is exception i.e., has higher ionization potential than aluminium because of ns² configuration which is stable.

Atomic radius: The distance from the centre of the nucleus to the outermost shell of electrons in the atom of any element is called its atomic radius.

Ionic radius: The effective distance from the centre of nucleus of an ion upto which it has an influence on its electron cloud is called its ionic radius.