The correct options are
C LiAlH4
D H2
Magnesium directly combines with hydrogen to form magnesium hydride.
Mg+H2Heat−−−→MgH2
Beryllium hydride is prepared by the reaction of beryllium dichloride with lithium aluminum hydride.
2BeCl2+LiAlH4→2BeH2+LiCl+AlCl3