How is dihydrogen prepared
a. from water by using a reducing agent?
b. in the laboratory in pure form?
c. from hydrocarbons?

Explanation

a. Dihydrogen is prepared by reacting a highely reacting metal like sodium with water.
`2Na_(s)+underset(("Cold"))(2H_(2)O_(l))to2NaOH_(aq)+H_(2(g))`
b. In the laboratory, dihygeon is prepared by electrolysis of acidified water using platinum electrode.
`2H_(2)O_(l)overset("Electrolysis")underset("Traces of acid/base")to2H_(2(g))+O_(2(g))`
At cathod: `2H^(o+)+2e^(ɵ)toH_(2)`
At anode: `4overset(Theta)(O)Hto2H_(2)O(l)+O_(2)(g)+4e^(ɵ)`
c. From hydrocarbons: Reaction of steam on hydrocarbons at higher temperatures:
`C_(n)H_(2n+2)+nH_(2)Ooverset(1270 K)underset("Catalyst")tonCO+(2n+1)H_(2)`
`CH_(4)+H_(2)Ooverset(1270 K)toCO+3H_(2)`
`C_(3)H_(8(g))+3H_(2)O_(g)tooverset(1270 K)underset("Catalyst")to2CO_(g)+7H_(2)O_(g)`