Question

why dilute nitric acid is not used to prepare hydrogen?

Answer 1

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Dilute Nitic Acid $\mathsf{(HNO_3)}$ is not used to prepare hydrogen because hydrogen gas is not evolved when a metal reacts with nitric acid.

It is 'cos $\mathsf{HNO_3}$ is a strong oxidising agent. It oxidises the $\mathsf{H_2}$ produced to water and itself gets reduced to any of the nitrogen oxides $\mathsf{(N_2O, \ NO, \ NO_2)}$.

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