Which element from following exhibits the highest number of allotropes?

Which of the following is a pair of dihydric phenols?

Calculate $$\Delta \mathrm{H}$$ for following reaction, at $$25{ }^{\circ} \mathrm{C}$$.

$$\mathrm{NH}_2 \mathrm{CN}_{(\mathrm{g})}+\frac{3}{2} \mathrm{O}_{2(\mathrm{~g})} \longrightarrow \mathrm{N}_{2(\mathrm{~g})}+\mathrm{CO}_{2(\mathrm{~g})}+\mathrm{H}_2 \mathrm{O}_{(\mathrm{g})}$$

$$(\Delta \mathrm{U}=-740.5 \mathrm{~kJ}, \mathrm{R}=8.314 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1})$$

What is number of atoms present in $$2.24 \mathrm{~dm}^3 \mathrm{~NH}_{3(\mathrm{~g})}$$ at STP?