Which one of the following items gives its correct total number?

$\int_{-2}^2 |[x]| \, dx$ is equal to

The cause of the potential barrier in a $P-N$ junction diode is

In an $LC$ circuit,the capacitor has a maximum charge $q_0$. The value of $\left. \frac{di}{dt} \right|_{\max }$ is:

$A$ pulley of radius $2\, m$ is rotated about its axis by a force $F = (20t - 5t^2)\, N$ (where $t$ is measured in seconds) applied tangentially. If the moment of inertia of the pulley about its axis of rotation is $10\, kg\, m^2$,the number of rotations made by the pulley before its direction of motion is reversed,is

Lichens indicate $SO_2$ pollution because they