Which pair of oxyacids of phosphorus contains ' $\mathrm{P}-\mathrm{H}$ ' bonds?

1. $\mathrm{H}_3 \mathrm{PO}_4, \mathrm{H}_3 \mathrm{PO}_3$
2. $\mathrm{H}_3 \mathrm{PO}_5, \mathrm{H}_4 \mathrm{P}_2 \mathrm{O}_7$
3. $\mathrm{H}_3 \mathrm{PO}_3, \mathrm{H}_3 \mathrm{PO}_2$
4. $\mathrm{H}_3 \mathrm{PO}_2, \mathrm{HPO}_3$

Asked in: AP EAMCET 2009

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