Which of the following circuits is reverse-biased?

$A$ potential barrier of $0.4 \,V$ exists across a p-n junction. An electron enters the junction from the $n$-side with a speed of $6.0 \times 10^{5} \,ms^{-1}$. The speed with which the electron enters the $p$-side will be $\frac{x}{3} \times 10^{5} \,ms^{-1}$. The value of $x$ is ..............
(Given: mass of electron $= 9 \times 10^{-31} \,kg$,charge on electron $= 1.6 \times 10^{-19} \,C$.)

Find the current $I$ in the circuit in $amp$.

Diffusion current in a $p-n$ junction is greater than the drift current in magnitude when:

If in a $p-n$ junction diode,a square input signal of $10\, V$ (varying from $+5\, V$ to $-5\, V$) is applied as shown,then the output signal across $R_L$ will be:

Two identical $P-N$ junctions are connected in series with a battery in three ways as shown in the figure. In which two circuits will the potential difference across the $P-N$ junctions be equal?