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Answer: (d) Cu

c) C₂D₂   product is formed when calcium carbide reacts with heavy water.

(a) The water-gas shift reaction (WGSR) describes the reaction of carbon monoxide and water vapour to form carbon dioxide and hydrogen (the mixture of carbon monoxide and hydrogen (not water) is known as water gas):

(b)( i)Same valency , diatomic molecules

(ii) Forms hydrides like halides

(iii) The ionization energy of Hydrogen and halogens are comparable.

(iv) Forms covalent bonds like halogens

Presence of calcium and magnesium salts in the form of hydrogencarbonate, Chloride and Sulphate in water makes water hard.

If the metal ions present in a sample of water interact with soap ,a sodium or potassium salt of a fatty acid and resist its dissolution in water  then froth/lather is not formed in that sample when soap is used. And the sample of water is called hard water.  Normally these ions are Ca²⁺,Mg²⁺,.Fe²⁺/Fe³⁺ . They may be present as chloride or sulphate or bicarbonate salt,

If the water sample is high in concentration of mineral acid then it can rsist the dissolution of soap in it and that is why the sample acts as hard water, The presence of other ions eg Zn²⁺, Al³⁺ etc can cause hardness in water.

To convert unsaturated fatty acid to saturatedfatty acid.

(i) H₂ + CO + RCH = CH₂ → RCH₂CH₂CHO aldehyde

(ii) H₂ + RCH₂CH₂CHO → RCH₂CH₂CH₂OH Alcohol

The size of hydrogen is smaller than that of sodium and therefore, the ionization enthalpy of H is higher (1312 kJ mol^-1) than that of Na (496 kJ mol^-1).

Basic property of hydrogen economy is that it can be converted into liquid by cooling under high pressure and therefore, can be transported.

• Ionisation enthalpy of hydrogen is higher than that of sodium as the atomic size of hydrogen is smaller than that of sodium atom. 

(i) NaH + H₂O → NaOH + H₂

(ii) 2LiH + B₂H₆ → 2LiBH₄

(C) If assertion is true, but reason is false.

(i) Hydrogen peroxide is used as a hair bleach and as a mild disinfectant. 

(ii) It is used in the manufacture of chemicals like sodium perborate and per-carbonate which are used in high quality detergents.

Use of H₂O₂: Hair bleach / mild disinfectant/ antiseptic/ to manufacture sodium perborate and percarbonate (detergents)/ bleaching agent for textiles, paper pulp, leather, oils. Nowadays it is also used in Environmental (Green) Chemistry.

a) In a structure of ice, Oxygen atom is tetrahedrally surrounded by four hydrogen (with two hydrogen by the hydrogen bond and with two hydrogen by covalent bond ) and have vacant spaces in which air is trapped 

b) Due to extensive hydrogen bonding in water 

c) NaH is ionic compound while water is a covalent compound

(i) 2Al(s) + 2NaOH(aq) + 2H₂O(l) → 2NaAlO₂(aq) + 3H₂(g) Dihydrogen(A)

(ii) Fe₃O₄(s) {Black solid(B)} + 4H₂(g) \(\overset{773\,K}{\longrightarrow}\) 3Fe(s) Grey metal(C) + 4H₂O Water(D)

(iii) Fe(s) + CuSO₄(aq) → FeSO₄(sq) + Cu(s)

(iv) 3Fe(s) + 8IINO₃(sq) → FeO.Fe₂O₃(s) {Ferrosoferri oxide(B)} + 8NO₂(g) + 4H₂O(l)

Iron is rendered passive due to the formation of ferrosoferric oxide or magnetic oxide {black solid (B)}

(d) sp³ and sp³

(a) Hydrogen

(a) Hydrogen

Answer: (b) 3

The most reactive alkali metals decompose water in the cold with the evolution of hydrogen and leaving an alkali solution.

2Na_(s) + 2H₂O_(I) → 2NaOH_(aq) + H_2(g)

(c) Beryllium

Hydrogen has a tendency to react with reactive metals like lithium, sodium to give corresponding hydrides

2Li+H₂ → 2LiH 

2Na+H₂ → 2NaH

These hydrides are used as reducing agents in synthetic organic chemistry. It is also used to prepare important hydrides such as lithium aluminium hydride and sodium boro hydride (organic reducing agents).

4LiH + AlCl₃ → Li[AIH₄] + 3LiCl 

4NaH + B(OCH₃)₃ → Na[BH₄] + 3CH₃ONa