Which of the following is not a colligative property?

Which sample contains a greater number of nuclei: a $5.00 \, \mu Ci$ sample of $^{240}Pu$ (half-life $6560 \, y$) or a $4.45 \, \mu Ci$ sample of $^{243}Am$ (half-life $7370 \, y$)?

What will be the $pH$ of an aqueous solution of $MgCl_2$?

Which of the following is an unsuitable habitat for algae?

$A$ particle of mass $m_1$ is moving with a velocity $v_1$ and another particle of mass $m_2$ is moving with a velocity $v_2$. Both of them have the same momentum,but their kinetic energies are $E_1$ and $E_2$ respectively. If $m_1 > m_2$,then:

Let $\overrightarrow{a}, \overrightarrow{b}, \overrightarrow{c}$ be the position vectors of the vertices $A, B, C$ respectively of $\triangle ABC$. The vector area of $\triangle ABC$ is :