Which of the following is the most abundant element in the universe?

When electric current is supplied through an ionic hydride in its fused state,then:

Which of the following substances will absorb oxygen rapidly?

The shape of the colourless neutral gas formed on thermal decomposition of ammonium nitrate is

Complete the following chemical reactions:
$(i) \ PbS_{(s)} + H_2O_{2_{(aq)}} \to $
$(ii) \ MnO_{4_{(aq)}}^{-} + H_2O_{2_{(aq)}} \to $
$(iii) \ CaO_{(s)} + H_2O_{(g)} \to $
$(iv) \ AlCl_{3_{(g)}} + H_2O_{(l)} \to $
$(v) \ Ca_3N_{2_{(s)}} + H_2O_{(l)} \to $
Classify the above into $(a)$ hydrolysis,$(b)$ redox and $(c)$ hydration reactions.

Observe the following reactions:
$I$. $CO_{(g)} + H_{2(g)} \xrightarrow{X} HCHO_{(g)}$
$II$. $CO_{(g)} + 3 H_{2(g)} \xrightarrow{Y} CH_{4(g)} + H_2O_{(g)}$
The catalysts $X$ and $Y$ in the above reactions are respectively: