Action of water or dilute mineral acids on metals can give

Which of the following is true for heavy water?

Which of the following sets are correctly matched?
$(i)$ $B_2H_6$ - electron deficient hydride
$(ii)$ $NH_3$ - electron precise hydride
$(iii)$ $H_2O$ - electron rich hydride

Which of the following cannot be used for the preparation of $H_2$?

What else is present in a fire extinguisher besides $H_2SO_4$?

Which property of hydrogen distinguishes it from alkali metals?