A tetrapeptide, " $x$ " on complete hydrolysis produced glycine (Gly), alanine (Ala), valine (Val), leucine (Leu) in equimolar proportion each. The number of tetrapeptides (sequences) possible involving each of these amino acids is :

Which among the following molecules is (a) involved in $\mathrm{sp}^3 \mathrm{~d}$ hybridization, (b) has different bond lengths and (c) has lone pair of electrons on the central atom?

In 3,3-dimethylhex-1-en-4-yne, there are _________$\mathrm{sp}^3$,_________$\mathrm{sp}^2$ and_________ sp hybridised carbon atoms respectively.

In Dumas' method for estimation of nitrogen, 0.5 gram of an organic compound gave 60 mL of nitrogen collected at 300 K temperature and 715 mm Hg pressure. The percentage composition of nitrogen in the compound (Aqueous tension at $300 \mathrm{~K}=15 \mathrm{~mm} \mathrm{Hg}$ ) is___________%.