The first step of taxonomy is .......... .

$A$ body cools from $62^{\circ}C$ to $50^{\circ}C$ in $10 \text{ minutes}$ and to $42^{\circ}C$ in the next $10 \text{ minutes}$. The temperature of the surroundings is ........ $^{\circ}C$.

$A$ ray of light is incident on the hypotenuse of a right-angled prism after travelling parallel to the base inside the prism. If $\mu$ is the refractive index of the material of the prism,the maximum value of the base angle for which light is totally reflected from the hypotenuse is

One ampere of current is passed for $9650 \ s$ through molten $AlCl_3$. What is the weight in grams of $Al$ deposited at cathode? (atomic weight of $Al = 27$)

Enzymes are

$\frac{1}{2 \cdot 3} + \frac{1}{4 \cdot 5} + \frac{1}{6 \cdot 7} + \frac{1}{8 \cdot 9} + \dots$ is equal to