Identify the salts X and Y from the following observations.

(a) Salt X is white in colour. On strong heating, it produces buff yellow residue and liberates reddish brown gas. Solution of salt X produces chalky white insoluble precipitate with excess of ammonium hydroxide.

(b) Salt Y is black in colour. On reacting with conc. HCl, it liberates a pungent greenish yellowish gas which turns moist starch iodide paper blue black.

Write the products and balance the equation.

(a) Na₂CO₃ + H₂SO₄ ⟶

(b) Fe + H₂SO₄ ⟶

Give reasons:

(a) Covalent compounds have low melting point.

(b) For covalent bond formation both atoms should have high ionisation.

(c) Covalent bond formation takes place when both atoms should have four or more electron in outermost shell.

Glucose or blood sugar has the molecular formula C₆H₁₂O₆. Determine % of each element.