Give balanced equations for obtaining hydrogen from ?

(a) Boiling water using a divalent metal

(b) Steam using a trivalent metal

(c) Steam using a metal – and the reaction is reversible.

State why hydrogen is not prepared in the laboratory by the action of –

(a) Sodium with cold water.

(b) Calcium with dilute sulphuric acid.

(c) Lead with dilute hydrochloric acid.

In the laboratory preparation of hydrogen from zinc and dil. acid. Give reasons for the following :

(a) The complete apparatus is air-tight.

(b) Dilute nitric acid is not preferred as the reactant acid.

(c) The lower end of the thistle funnel should dip below the level of the acid in the flask.

(d) Hydrogen is not collected over air.

'Magnesium reacts with very dilute nitric acid at low temperatures liberating hydrogen.' Give reasons.