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.

How are the unreacted gases separated out in 'Bosch process' in the manufacture of hydrogen.

Compare the combustibility of –

(a) pure hydrogen

(b) hydrogen-air mixture.