Hydrogen

This is a multiple choice answer as classified in NCERT Exemplar

Option (i) and (ii)

When an electron is removed from a hydrogen atom, the nucleus decreases to 1.5 * 10^-3 pm in size. When compared to usual atomic and ionic sizes of 50 to 200 pm, this is exceedingly small. As a result, H+ does not exist independently and is always bound to other atoms or molecules.

This is a multiple choice answer as classified in NCERT Exemplar

Option (i) and (iii)

Heavy water is utilised as a moderator in nuclear reactors and exchange reactions, and it is more associated with water due to its higher mass.

This is a multiple choice answer as classified in NCERT Exemplar

Option (i) and (ii)

The combination of CO and H₂ is known as water gas. This mixture of CO and H₂ is also known as synthesis gas or 'syngas' since it is used to make methanol and other hydrocarbons.

This is a multiple choice answer as classified in NCERT Exemplar

Option (iii) and (iv)

H⁺ does not exist freely and is always associated with other atoms or molecules. It has an extremely high ionisation enthalpy and does not have metallic properties under normal conditions, unlike alkali metals.

This is a multiple choice answer as classified in NCERT Exemplar

Option (i)

Group 6

From group 6, only chromium forms CrH.

This is a multiple choice answer as classified in NCERT Exemplar

Option (i)

Groups 7,8, 9

Explanation: The metals belonging to group 7, 8 and 9 do not have tendency to form hydrides.

This is a multiple choice answer as classified in NCERT Exemplar

Option (iii)

Na₆P₆O₁₈

Sodium hexametaphosphate (Na₆P₆O₁₈), commercially called 'calgon', is used to remove hardness from water.

This is a multiple choice answer as classified in NCERT Exemplar

Option (i)

Ca²⁺

Water becomes 'hard' when it contains calcium and magnesium salts in the form of hydrogen carbonate, chloride, and sulphate.

This is a multiple choice answer as classified in NCERT Exemplar

Option (iv)

CO (g)+2H₂ (g) → CH₃OH (l)

The reaction shown in equation (iv) shows the synthesis of methanol from water gas.

This is a multiple choice answer as classified in NCERT Exemplar

Option (ii)

Sulphuric acid

2HSO₄^- (aq) → HO₃SOOSO₃H (aq) → 2HSO₄^- (aq)+2H⁺ (aq) + H₂O₂ (aq)