The most dangerous method of preparing hydrogen would be by the action of $HCl$ and

Which of the following statements about $H_2SO_4$ is incorrect?

How many isotopes of Hydrogen are there? Give their names.

Complete the following reactions:
$(i) \, H_{2(g)} + M_m O_{o(s)} \xrightarrow{\Delta }$
$(ii) \, CO_{(g)} + H_{2(g)} \xrightarrow[catalyst]{\Delta }$
$(iii) \, C_3 H_{8(g)} + 3 H_2 O_{(g)} \xrightarrow[catalyst]{\Delta }$
$(iv) \, Zn_{(s)} + NaOH_{(aq)} \xrightarrow{heat}$

The difference between heat of adsorption of ortho and para hydrogen is $......... \ kJ \ mol^{-1}$.

Which will not cause any atmospheric pollution?