The equivalent resistance of the following circuit when no current flows in the resistance of $5 \Omega$ is nearly

In the case of common emitter transistor amplifier, the ratio of collector current to emitter current is 0.96 , then the current gain $(\beta)$ of the amplifier is

Which of the following comes under the category of random errors?

The energy that should be added to an electron to reduce its de-Broglie wavelength from $\lambda$ to $\frac{\lambda}{2}$ is $n$ times the initial energy. The value of ' $n$ ' is