$A$ thermodynamic system is taken through the cycle $PQRS P$ process as shown in the figure. The net work done by the system is ......... $J$.

Which one of the following is heterosporous?

The number of ways of choosing $10$ objects out of $31$ objects,of which $10$ are identical and the remaining $21$ are distinct,is

If $\alpha, \beta$ and $\gamma$ are the lengths of the altitudes of a $\triangle ABC$ with area $\Delta$,then $\frac{\Delta^2}{R^2}\left(\frac{1}{\alpha^2}+\frac{1}{\beta^2}+\frac{1}{\gamma^2}\right)$ is equal to

In green plants,cell elongation in the internodal regions is caused by which of the following?

Identify the order in which the spin-only magnetic moment (in $BM$) increases for the following four ions:
$I. Fe^{2+}$
$II. Ti^{2+}$
$III. Cu^{2+}$
$IV. V^{2+}$