The structure which prevents the entry of food into the respiratory tract is

If $\alpha = \frac{5}{2! 3} + \frac{5 \cdot 7}{3! 3^2} + \frac{5 \cdot 7 \cdot 9}{4! 3^3} + \ldots$,then $\alpha^2 + 4\alpha$ is equal to

Which complex is most stable?
Where $k_d = \text{Dissociation constant}$

Wavelengths of light used in an optical instrument are $\lambda_1 = 4000 \ Å$ and $\lambda_2 = 5000 \ Å$. The ratio of their respective resolving powers (corresponding to $\lambda_1$ and $\lambda_2$) is:

Which of the following is most reactive towards alcoholic $KOH$?

What are enzymes composed of?