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(D) If both assertion and reason are false.

(i) Ca⁺⁺ ions in the form of Ca(HCO₃)₂ or CaCl₂ or CaSO₄ cause hardness in water,i.e.,soluble salts of calcium can cause hardness in water.  

The process of removal of Ca²⁺ and Mg²⁺ ions from water is called softening of water.

H₂O₂ is prepared by treatment of metal peroxide with acid. 

For example: BaO₂+H₂SO₄→BaSO₄+H₂O₂ 

H₂O₂ is very effective oxidising agent for example : PbS+4H₂O₂→PbSO₂+4H₂O Hydrogen peroxide acts as reducing agent also. Hydrogen peroxide forms salt with bases, which confirms its acidic character

H₂O₂+2NaOH→Na₂O₂+2H₂O

Water is amphoteric in nature and it behaves both as an acid as well as a base. With acids stronger than itself (eg., H₂S) it behaves as a base and with bases stronger than itself (eg. NH₃) it acts as an acid.

(i) As a base: H₂O(l) +H₂S(aq) → H₃O + (aq) +HS^-(aq) 

(ii) As an acid: H₂O(l) +NH₃(aq) → OH^-(aq) + NH₄⁺ (aq)

Hydrogen peroxide is decomposed by the rough surfaces of glass, alkali oxides present in it and light. Therefore, to prevent its decomposition, H₂O₂ is usually stored in coloured paraffin wax coated plastic or Teflon bottles.

Metallic hydrides are usually obtained by hydrogenation of metals and alloys in which hydrogen occupies the interstitial sites (voids). Hence, they are called interstitial hydrides. 

e.g., PdH.

The hydrides are classified as Ionic, Covalent and Metallic Hydrides. 

Ionic hydride – LiH 

Covalent hydride – CH₄ 

Metallic hydride -TiH

(a) reaction of granulated zinc with dilute H₂SO₄

Industrially, H₂O₂ is prepared by the auto oxidation of 2-ethylanthraquinol to 2-ethylanthraquinone. H₂O₂ is stored in wax-lined glass or plastic bottles so that it does not decompose into H₂O and O₂. 

Because it is decomposed to H₂O and O₂ when comes in contact with sunlight.

Ternary hydrides are compounds in which the molecule is constituted by hydrogen and two types of elements.

e.g., LiBH₄ or LiAlH₄.

(c) Hydrogenation

(b) Ortho isomer has zero nuclear spin whereas the para isomer has one nuclear spin 

Correct statement: 

Ortho isomer – one nuclear spin Para isomer – zero nuclear spin

(a) Statements-I and II are correct and Statement-II is the correct explanation of statement-I.

(c) Hydrogen has three isotopes of which tritium is the most common.

Correct statement: 

Hydrogen has three isotopes of which protium is the most common.

(a) Metallic hydride

1. They are the compounds in which hydrogen is attached to another element by sharing of electrons. 

2. The most common examples of covalent hydrides are methane, ammonia, water and hydrogen chloride. 

3. Molecular hydrides of hydrogen are further classified into three categories as,

• Electron precise (CH₄, C₂H₆ , SiH₄ , GeH₄) 
• Electron-deficient (B₂ H₆) and 
• Electron-rich hydrides (NH₃, H₂O)

4. Since most of the covalent hydrides consist of discrete, small molecules that have relatively weak intermolecular forces, they are generally gases or volatile liquids.

(c) (i) and (ii)

Answer: Water

(c) 75% ortho form + 25% para form

The aqueous solution of hydrogen peroxide is spontaneously disproportionate to give oxygen. The reaction is slow but it is explosive when it is catalyzed by metal or alkali dissolved from glass. For this reason, its solution are stored in plastic bottles.

H₂O_2(aq) → H₂O_(I) + \(\frac{1}{2}\)O_2(g)

(d) Hydrogen

(d) group one elements 

e.g., Sodium hydride (Na⁺H^- )

Answer: (C) CO + H₂ 

(a) A-4, B-3, C-1, D-2

A binary hydride is a compound formed by hydrogen with other electropositive elements including metals and nonmetals.

e.g., LiH or MgH₂.

(a) 1 ml of H₂O₂ will give 100 ml O₂ at STP 

(b) Vanderwaals bond < Hydrogen bond < Covalent, bond

(d) Platinum

The oxidising property of hydrogen peroxide and harmless nature of its products such as water and oxygen, leads to oxidation of pollutants in water and act as a mild antiseptic.