Which of the following statements is most applicable to hydrogen?

Number of nucleons in $D_2$ molecule is

Ionisation of $H$-atom would produce

Which of the following acids exhibits oxidizing,reducing,and complex-forming properties?

Dehydration of oxalic acid with concentrated $H_2SO_4$ produces ............

Arrange the following:
$(i)$ $CaH_{2}$,$BeH_{2}$,and $TiH_{2}$ in order of increasing electrical conductance.
$(ii)$ $LiH$,$NaH$,and $CsH$ in order of increasing ionic character.
$(iii)$ $H-H$,$D-D$,and $F-F$ in order of increasing bond dissociation enthalpy.
$(iv)$ $NaH$,$MgH_{2}$,and $H_{2}O$ in order of increasing reducing property.