Which of the following is an amphoteric hydroxide?

$A$ 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 $6 \ Rs$.)

If $\cos ^{-1}\left(\frac{x^2-y^2}{x^2+y^2}\right)=k$ (a constant),then $\frac{d y}{d x}$ is equal to

Ribose is an example of

If $f(x) = \frac{x^2}{x+a}$, then $f^{\prime \prime}(a)$ is equal to

Earthworms are ........