What is Carbogen?

Ortho and para hydrogen differ in

Pure dihydrogen $(99.95\%)$ is obtained by the electrolysis of

What is believed to be the second most common element in the universe?

Which one of the following statements is incorrect $?$

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 $H_2O$ in order of increasing reducing property.