Select the taxon mentioned that represents both marine and fresh water species.

Crystalline sodium chloride is an insulator of electricity because $......$

$A$ certain radioactive substance reduces to $25\%$ of its initial value in $16$ days. Its half-life is ........ $days$.

The coefficient of $x^4$ in the expansion of $\frac{(1-3x)^2}{(1-2x)}$ is equal to

The time in seconds required to produce a potential difference of $20 \ V$ across a capacitor of $1000 \ \mu F$ when it is charged at a steady rate of $200 \ \mu C/s$ is:

According to molecular orbital theory,the total number of bonding electron pairs in $O_2$ is