Acidity of diprotic acids in aqueous solutions increases in the order

Boron can be obtained by various methods but not by :

The pattern of standing waves formed on a stretched string at two instants of time (extreme and mean positions) is shown in the figure. The velocity of the two waves superimposing to form stationary waves is $360 \ m/s$ and their frequency is $256 \ Hz$. Which of the following is not a possible value of $t$ (in $sec$)?

When the temperature of a body increases from $T$ to $T+\Delta T$,its moment of inertia increases from $I$ to $I+\Delta I$. If $\alpha$ is the coefficient of linear expansion of the material of the body,then $\frac{\Delta I}{I}$ is (neglect higher orders of $\alpha$ ).

The rearrangement of phenyl esters to $o-$ and $p-$ hydroxy ketones in the presence of $AlCl_3$ is known as:

Choanocytes are present in