Soil erosion can be prevented by

What is the gas liberated when alkaline formaldehyde solution is treated with $H_2O_2$?

Which of the following metals is the most reactive?

Which of the following is the strongest Bronsted base?

$A$ sample of a radioactive element has a mass of $10 \, g$ at an instant $t=0$. The approximate mass of this element in the sample after two mean lives is ........ $g$.

$A$ disc has mass $M$ and radius $R$. How much tangential force should be applied to the rim of the disc,so as to rotate with angular velocity $\omega$ in time $t$?