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The chemical reaction in which two or more products are formed from a single reactant is called decomposition reaction.

The chemical formula of Gypsum: CaSO₄.2H₂O

When gypsum is heated at 373k, we get plaster of Paris

Chemical equation: 
                            Δ
CaSO₄.2H₂O  ---------->CaSO₄.1/2H₂O  +3/2 H₂O

So, Calcium Sulphate Hemi hydrated salt --- CaSO₄.1/2H₂O is produced after heating gypsum.

Plaster of paris is used in case of fracture.

• Analytical chemistry facilitates the investigation of the chemical composition of substances.
• It uses the instruments and methods to separate, identify and quantify a sample under study.

Thus,

Analytical chemistry provides chemical or physical information about a sample.

The observed value is 3.8 g and accepted (true) value is 3.92 g.

i. Absolute error = Observed value – True value

= 3.8 – 3.92

= -0.12 g

ii. Relative error = \(\frac{Absolute\,error}{True\,value}\) x 100%

= \(\frac{-0.12}{3.92}\) x 100%

= - 3.06%

[Note : The negative sign indicates that experimental result is lower than the true value.]

∴ i. Absolute error = - 0.12 g

ii. Relative error = - 3.06%

The chemical analysis of a sample is carried out mainly in two stages : 

By the dry method and by the wet method. 

In dry method, 

The sample under test is not dissolved and in wet method, the sample under test is first dissolved and then analysed to determine its composition.

A) Burning of L.P.G.

Correct option is (c) N, O, F

Elements on two extremes of a period easily combines with oxygen to oxides. The normal oxide formed by the element on extreme left is the most basic (eg. Na₂O) whereas that formed by the element on extreme right is the most acidic (eg. cl₂ O₇). Oxides at the centre are however amphoteric (eg. Al₂ O₃) or neutral (eg. CO).

The reaction in which a compound is decomposed by heating it to a high temperature is called thermal decomposition.

False

The thermal decomposition reaction of calcium sulphate (gypsum) is not used in black and white photography. The reaction of silver bromide with sunlight to for silver and bromine used in black and white photography. 

Hence, the give statement is false.

(b) CaSO₄.\(\frac{1}{2}\)H₂O 

• Gypsum have low thermal conductivity. 
• It won’t allow the electric current to pass through it. So it is known as natural insulator.

A) AgNO₃ + NaCl → AgCl + NaNO₃ 

• The number of electrons that an atom of an element gives away, takes up or shares forming a bond is called the valency of that element.
• These electrons are always in whole numbers and not in fractions.
• Therefore, valency is always a whole number.

Correct option is (a) Al₂O₃ < MgO < Na₂O < K₂O

(a) CaSO₄.2H₂O 

Carbon is formed in the thermal decomposition of sugar.

(i) The above reaction is a double displacement reaction.

(ii) AgNO₃ and NaCl are the reactants while AgCl and NaNO₃ are the products.

(iii) The reactants and the product NaNO₃ are in aqueous state. The product AgCl is formed in the form of precipitate.

• The electronic configuration of Magnesium (Mg) is (2,8,2), it has 2 electrons in its 3rd orbit. 
• It tends to give these ‘2’ electrons so that it is left up with (2, 8), having 8 electrons in the second orbit, with a stable state. 
• The loss of two electrons leads to the formation of Magnesium ion (Mg₂⁺) which is double positively charged as it has lost two electrons.

The size of an atom is determined by its radius.

Correct answer: (c) atomic mass number

(1) Combination reaction

(2) Decomposition reaction

(3) Displacement reaction

(4) double displacement reaction

(5) Combination reaction

(6) double displacement reaction

Correct answer: (a) Mole

O can not form 6 bonds due to absence of d orbitals. 

The formula to determine the number of moles of a substance is as given below.

Number of moles of a substance (n) = \(\cfrac{Mass\,of\,substance\,in\,grams\,(m)}{Molecular\,mass\,of\,substance(M)}\)

Due to less degree of dissociation of H₂S than H₂Te.

Unified mass is the standard unit of atomic mass that quantifies mass on an atomic or molecular scale. Its symbol is ‘u’.

1 u = 1.66053904 x 10^-27 kg.

The number of protons and neutrons in the atomic nucleus is called the atomic mass number.

The size of an atom is determined by its radius. The atomic radius of an isolated atom is the distance between the nucleus of an atom and its outermost orbit.

• The atomic size of an element depends on the number of electron orbits in the atom of that element. 
• If 2 atoms have the same outermost orbit, then the atom having the larger number of electrons in the outermost orbit is smaller than the one having fewer electrons in the same outermost orbit. 
• Atomic number of sodium (Na) is 11. Hence, its electronic configuration is (2, 8, 1) while atomic number of magnesum (Mg) is 12 and hence its electronic configuration is (2, 8, 2). 
• As compared to sodium atom Magnesum atom has larger number of electrons n its electronic configuration.
• Therefore, atomic size of sodium is bigger than atomic size of Magnesium.

• The mass of an atom is concentrated in its nucleus and it is due to the protons (p) and neutrons (n) in it.
• Since an atom is very very tiny, it was not possible to measure atomic mass accurately. Therefore, the concept of relative mass of an atom was formed.
• To express relative mass of an atom, reference of atom is considered. The two reference atoms were as follows:

(a) Hydrogen (H) atom: The hydrogen atom is the lightest. The relative mass of a hydrogen atom is 1 which has only 1 proton in its nucleus. On this scale, the relative atomic mass of many elements comes out to be fractional. Therefore, carbon was selected as a reference atom.

(b) Carbon (C) atom: The carbon atom is selected as reference atom. In this scale, the relative mass of a carbon atom is accepted as 12.

• The relative atomic mass of 1 hydrogen (H) atom compared to the carbon (C) atom becomes

(i) Exothermic reaction

(ii) Exothermic reaction

(iii) Endothermic reaction

(iv) Exothermic reaction

(v) Endothermic reaction

(vi) Exothermic reaction

(vii) Endothermic reaction

(viii) Exothermic reaction

Electron gain enthalpy of oxygen = -141 kJ /mol 

Electron gain enthalpy of S = -200 kJ /mol

Thus electron gain enthalpy of S is more than O. This is due to greater inter electronic repulsion in O than S which results owing to smaller size of O than S.

Step 1:

Rewrite the given equation as it is 

Ba(OH)₂ + HBr → BaBr₂ + H₂O

Step 2:

write the number of atoms of each element in the unbalanced equation on both sides of the equation.

Step 3:

To balance the number of oxygen atoms:

To equalise the number of oxygen atoms, we use 2 as the coefficient of H₂O in the product.

Now, the partly balanced equation become as follows

Ba(OH)₂ + HBr → BaBr₂ + 2H₂O

Step 4:

Now, balance the number of hydrogen atoms. In the partly balanced equation:

To equalise the number of hydrogen atoms, we use 2 as the coefficient of HBr in the reactants. Now, the equation becomes

Ba(OH)₂ + 2HBr → BaBr₂ + 2H₂O

Now, count the atoms or each element on both sides of the equation. The number of atoms on both sides are equal. Hence, the balanced equation is

Ba(OH)₂ + 2HBr → BaBr₂ + 2H₂O

Now indicate the physical states of the reactants and products.

Ba(OH)_2(aq) + 2HBr_(aq) → BaBr_2(aq) + 2H2O_(l)

Due to larger atomic size of S less repulsion in S-S bond than O-O bond. 

Due to formation of Pπ-Pπ bond oxygen exists as O=O molecule, where as sulphur exists as S₈.

Due to more electron electron repulsion in O.

• A mole is that quantity of a substance whose mass in grams is equal in magnitude to the molecular mass of that substance in Daltons.
• For example: Atomic mass of oxygen atom (O) is 16u. Thus, the molecular mass of oxygen molecule (O₂) is 16 x 2 = 32u. Therefore, 32 g of oxygen is 1 mole of oxygen.

Step 1:

Rewrite the given equation as it is

H₂SO_4(aq) + NaO_(aq) → Na₂SO_4(aq) + H₂O_(I)

Step 2:

write the number of atoms of each element in the unbalanced equation on both sides of the equation.

The number of oxygen atoms involved in different compounds on both sides (reactants and products) are equal. Therefore, balance the number of atoms of the second element, sodium.

Step 3:

To balance the number of sodium atoms:

To equalise the number of sodium atoms, we use 2 as the factor of NaOH in the reactants. Now, the partly balanced equation becomes as follows

H₂SO₄ + 2NaOH → Na₂SO₄ + H₂O

Step 4:

Now, balance the number of hydrogen atoms:

To equalise the number of hydrogen atoms, we use 2 as the factor or H₂O in the products. The equation then becomes

H₂SO₄ + 2NaOH → Na₂SO₄ + H₂O

Now, count the atoms of each element on both sides of the equation. The number of atoms on both sides are equal. Hence, the balanced equation is

H₂SO₄ + 2NaOH → Na₂SO₄ + H₂O

Now indicate the physical states of the reactants and the products.

H₂SO_4(aq) + 2NaOH_(aq) → Na₂SO_4(aq) + 2H₂O_(I)

• During earlier time, relative mass of an atom was considered for measuring the mass of an atom directly. But since the founding of unified mass, relative mass is not accepted henceforth.
• Unified atomic mass is the unit of atomic mass called as Dalton.
• Its symbol is ‘u’. lu = 1.66053904 x 10^-27 kg.

Option : (a) Fluorine

Correct option is B) C, Ni, Cr

Due to formation of pi bond.

Correct option is: (b) endothermic

Physical properties of sodium hydroxide:

• Sodium hydroxide (NaOH) is a white deliquescent solid.
• It has a melting point of 591 K.
• It is highly water soluble and gives a strongly alkaline solution.
• The surface of sodium hydroxide solution absorbs atmospheric CO₂ to form Na₂ CO₃.

(D) Sodium arsenite

Correct option is: (a) exothermic

i. Properties of white phosphorus:

• It is translucent white waxy solid. 
• It glows in the dark (chemiluminescence). 
• It is insoluble in water but dissolves in boiling NaOH solution.
• It is poisonous.

ii. Properties of red phosphorus:

• It is stable and less reactive. 
• It is odourless and possess iron grey lustre. 
• It does not glow in the dark. 
• It is insoluble in water. 
• It is nonpoisonous.

Correct option is (B) dioxygen

(B) Carbon dioxide