When an alkali metal is reacted with hydrogen then metallic hydride is formed. In this reaction:

The correct option is B hydrogen is reduced

Let M represents an alkali metal.

$2M+H_2\to 2MH$
$MH$ can be represented as $M^{+}+H^{-}$

In this reaction, conversion of hydrogen an be represented as $H_2+2e^{-}\to 2H^{-}$

Thus, a molecule of hydrogen accepts a pair of electrons to form 2 hydride ions. Gain of electrons is reduction. Hence, hydrogen is reduced to hydride ions.

Note: Alkali metal is oxidised to $M^{+}$ ions.