Which phylum is characterized by the presence of a central cavity known as the spongocoel?

Two persons $A$ and $B$ are located in the $X-Y$ plane at the points $(0,0)$ and $(0,10)$ respectively. (The distances are measured in $MKS$ units). At time $t=0$,they start moving simultaneously with velocities $\overrightarrow{v}_A = 2\hat{j} \text{ m/s}$ and $\overrightarrow{v}_B = 2\hat{i} \text{ m/s}$ respectively. The time after which $A$ and $B$ are at their closest distance is

Observe the following statements :
$I$. Bleaching powder is used in the preparation of chloroform.
$II$. Bleaching powder decomposes in the presence of $CoCl_2$ to liberate $O_2$.
$III$. Aqueous $KHF_2$ is used in the preparation of fluorine.
The correct combination is :

Identify $A$ in the following reaction.
$A + \text{Acetic anhydride} \xrightarrow{H^{+}} \text{Aspirin} + \text{Acetic acid}$

In a permanent magnet at room temperature,