Which of the following is a bad conductor of electricity?

The de-Broglie wavelength of an electron having $80 eV$ energy is nearly ($1 eV = 1.6 \times 10^{-19} J$,Mass of the electron $= 9 \times 10^{-31} kg$,Planck's constant $= 6.6 \times 10^{-34} J-s$) (in $\text{ Å}$)

Starting from rest, the time taken by a body sliding down on a rough inclined plane at $45^{\circ}$ with the horizontal is twice the time taken to travel on a smooth plane of the same inclination and same distance. Then the coefficient of kinetic friction is:

$A$ Zener diode,having a breakdown voltage equal to $15\,V,$ is used in a voltage regulator circuit as shown in the figure. The current through the diode is ........ $mA$.

$A$ $10 \mu F$ capacitor is charged by a $100 \text{ V}$ battery. It is disconnected from the battery and is connected to another uncharged capacitor of capacitance $30 \mu F$. During this process,the electrostatic energy lost by the first capacitor is

If $x = \log_{5}(1000)$ and $y = \log_{7}(2058)$,then: