Which of the following compounds undergoes sulfonation most easily?

Which of the following statements are correct?
$I$. $P_4$ molecule is very reactive because of angular strain.
$II$. The basicity of $H_3PO_3$ is $3$.
$III$. In gas phase,all $P-Cl$ bonds of $PCl_5$ have same bond length.
$IV$. In solid state,$PCl_5$ exists as an ionic solid,in which anion $[PCl_6]^-$ has octahedral and cation $[PCl_4]^+$ has tetrahedral shape.

In any $\triangle ABC$,$a(b \cos C - c \cos B)$ equals

Identify the glycosidic linkage present in lactose.

Syngamy means:

If $a, b, c$ are in $AP$,and $b-a, c-b, a$ are in $GP$,then $a: b: c$ is