Which of the following is the most stable carbocation?

In the compound $M-O-H$,the $M-O$ bond will be broken if

Reduction of nitrobenzene with $Zn$ and alcoholic $KOH$ solution results in the formation of the following compound:

If $\alpha = \frac{5}{2! 3} + \frac{5 \cdot 7}{3! 3^2} + \frac{5 \cdot 7 \cdot 9}{4! 3^3} + \ldots$,then $\alpha^2 + 4\alpha$ is equal to

$A$ uniform rod of mass $M$ and length $L$ is placed on a smooth horizontal surface. $A$ particle of mass $m$ moving with velocity $v$ strikes the rod at one end perpendicular to the rod. After the collision,the particle comes to rest. The velocity of the centre of mass of the rod after the collision is:

The phalangeal formula for the human hand is: