Molecular hydrogen is obtained from gaseous hydrogen atoms. Favourable conditions for the formation of hydrogen molecule according to Leachatelier's principle are

2Hg⇋H2g ;Formation of molecule from atoms involves bond formation. The process is exothermic. It is favoured at low ‘T’.∆ng=1-2=-1;Formation of H2(g) molecule involves decreases in number of moles. It is favoured at high ‘P’