MCQ
Which acid on heating produces phosphine ?
- Aphosphoric acid
- ✓phosphorous acid
- CPeroxymonophosphoric acid
- Dmetaphosphoric acid
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$2 \mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{O}_{2}+4 \mathrm{H}^{\oplus}+4 \mathrm{e}^{-} ; \mathrm{E}_{\mathrm{red}}^{0}=1.23 \mathrm{V}$
$(\mathrm{R}=8.314 \;\mathrm{J} \mathrm{mol}^{-1} \mathrm{K}^{-1} ; \text { Temperature }=298 \;\mathrm{K} ;$ oxygen under std. atm. pressure of $1 \;bar$)

[$A$] the physical state of $\mathrm{X}_2$ at atom temperature changes from gas to solid down the group
[$B$] decrease in $HOMO-LUMO$ gap down the group
[$C$] decrease in $\pi^*-\sigma^*$ gap down the group
[$D$] decrease in ionization energy down the group