Which of the following will be dissolved in excess of $NaOH$?

Four reactions are given below:
$(i)$ $2Li + 2H_2O \to 2LiOH + H_2$
$(ii)$ $2Na + 2H_2O \to 2NaOH + H_2$
$(iii)$ $2LiNO_3 \xrightarrow{\text{Heat}} 2LiNO_2 + O_2$
$(iv)$ $2NaNO_3 \xrightarrow{\text{Heat}} 2NaNO_2 + O_2$
Which of the above,if any,is wrong?

Magnesium wire is heated in the atmosphere of $CO_2$ because

What happens when : $(i)$ sodium metal is dropped in water? $(ii)$ sodium metal is heated in free supply of air? $(iii)$ sodium peroxide dissolves in water?

Write down the biological importance of $Na$ and $K$ in the human body and give a brief note on the sodium-potassium pump.

$A$ metal $M$ on heating in nitrogen gas gives $Y$. $Y$ on treatment with $H_2O$ gives a colourless gas which when passed through $CuSO_4$ solution gives a blue colour. $Y$ is