Which of the following is correctly matched?

Three rings each of mass $M$ and radius $R$ are arranged as shown in the figure. The moment of inertia of the system about the axis $YY'$ is:

$A$ semiconductor $X$ is made by doping a germanium crystal with arsenic $(Z = 33)$. $A$ second semiconductor $Y$ is made by doping germanium with indium $(Z = 49)$. The two are joined end to end and connected to a battery as shown. Which of the following statements is correct?

If $^nP_4 = 30 \times ^nC_5$,then $n = \dots$

Phosphorus pentachloride in the solid state exists as:

Two sides of a triangle are given by the roots of the equation $x^2-5x+6=0$ and the angle between the sides is $\frac{\pi}{3}$. Then,the perimeter of the triangle is