What distinguishes an insect from a crustacean?

Exhausted permutit does not contain $.......$ ion.

Four resistors $A, B, C$ and $D$ form a Wheatstone bridge as shown in the figure. The bridge is balanced when $C = 100 \Omega$. If $A$ and $B$ are interchanged,the bridge balances for $C = 121 \Omega$. The value of $D$ is (in $\Omega$)

The area bounded by the curves $y = x(x - 3)^2$ and $y = x$ is (in sq. units) :

An unbiased coin is tossed to get $2$ points for turning up a head and $1$ point for the tail. If three unbiased coins are tossed simultaneously,then the probability of getting a total of an odd number of points is

The structure of $PCC$ is