Which is distilled first?

Which of the following is a synthesis gas?

The hydride ion $H^{-}$ is isoelectronic with which of the following?

Ortho-hydrogen and para-hydrogen resemble in which of the following properties?

Which of the following statements are $NOT$ correct?
$A$. Hydrogen is used to reduce heavy metal oxides to metals.
$B$. Heavy water is used to study reaction mechanism.
$C$. Hydrogen is used to make saturated fats from oils.
$D$. The $H-H$ bond dissociation enthalpy is lowest as compared to a single bond between two atoms of any elements.
$E$. Hydrogen reduces oxides of metals that are more active than iron.
Choose the most appropriate answer from the options given below:

Which of the following is distilled first during the fractional distillation of liquid air or mixtures of these gases?