Which of the following salts increases the rate of the setting process of Plaster of Paris?

$A$ household refrigerator with a coefficient of performance $1.2$ removes heat from the refrigerated space at the rate of $60 \ kJ/min$. What would be the cost of running this fridge for one month ($30$ days)? (Assume it is used for $4$ hours each day and the cost of one electrical unit is $6 \ Rs$.)

The correct order of increasing ionic character is:

If $f(x) = x \tan^{-1} x$,then $\lim_{x \rightarrow 1} \frac{f(x) - f(1)}{x - 1}$ is equal to

$\sum_{k=1}^{\infty} \frac{1}{k!}\left(\sum_{n=1}^k 2^{n-1}\right)$ is equal to

In good conductors of electricity,the type of bonding that exists is