In the laboratory, for the prepration of dihydrogen gas form granular zinc, conc `H_(2)SO_(4)`, conc `HCl` and `HNO_(3)` cannot be used. Why? Which is the most suitable acid?

Explanation

For the prepartion of dihydrogen gas from granular zinc, conc `H_(2)SO_(4)`, conc `HCl` and `HNO_(3)` cannot be used due to :
(a) A part of conc `H_(2)SO_(4)` reacts with `H_(2)` and gets reduced to sulphur dioxides, `SO_(2)`
`H_(2)SO_(4)+H_(2)to2H_(2)+SO_(2)uarr`
(b) When conc `HCl` is used, dihydrogen liberated by the action of conc `HCl` on granular zinc will be impure as it contains fumes of volatile `HCl`. moreover, `ZnCl_(2)` formed is insoluble in conc `HCl`. it fomes a coating on granular zinc and reaction stops after sometime.
`Zn+2HCl to ZnCl_(2)+H_(2)uarr`
`HNO_(3)` acts both as an acid and as an oxidising agent. the nascent hydrgoen first formed reduces the nitric acid into varius oxides.
`2HNO_(3)+2Hto2NO_(2)+2H_(2)O`
`2HNO_(3)+6Hto2NO+4H_(2)O`
The most suitable acid is dilute `H_(2)SO_(4)`.