Which has the maximum number of molecules among the following?

Which of the following statements is not true?

In the arrangement shown in the figure,the pulley is smooth and massless,and all the strings are light. Let $F_1$ be the force exerted on the pulley in case $(i)$ and $F_2$ be the force in case $(ii)$. Then:

$Na^+$,$Mg^{2+}$,$Al^{3+}$,and $Si^{4+}$ are isoelectronic. What is the order of their ionic radii?

$A$ body is projected at an angle $\theta$ so that its range is maximum. If $T$ is the time of flight,then the value of maximum range is (acceleration due to gravity $= g$)

If the equilibrium constant for the reaction $2 AB \rightleftharpoons A_2 + B_2$ is $49$,what is the equilibrium constant for $AB \rightleftharpoons \frac{1}{2} A_2 + \frac{1}{2} B_2$?