In the diodes shown in the diagrams,which one is reverse biased?

In an unbiased $p-n$ junction diode:

$Ge$ and $Si$ diodes start conducting at $0.3\,V$ and $0.7\,V$ respectively. In the following figure,if the $Ge$ diode connection is reversed,the value of $V_0$ changes by: ...... $V$ (assume that the $Ge$ diode has a large breakdown voltage).

In the following circuit,find $I_1$ and $I_2$.

For diode $D_1$,the forward bias resistance is $20 \ \Omega$ and the reverse bias resistance is $600 \ \Omega$. For diode $D_2$,the forward bias resistance is $30 \ \Omega$ and the reverse bias resistance is $200 \ \Omega$. Find the equivalent resistance between $A$ and $B$ if $(i)$ $A$ is at a higher potential,and $(ii)$ $B$ is at a higher potential.

$A$ diode is connected to $220 \, V \, (rms) \, ac$ in series with a capacitor as shown in the figure. The voltage across the capacitor is