Reverse bias applied to a junction diode

In the given circuit,two ideal diodes are connected in parallel in opposite directions. What is the current $I$ flowing in the circuit (in $A$)?

In an unbiased $p-n$ junction:

Consider a circuit consisting of a capacitor $(20 \mu\text{F})$, a resistor $(100 \Omega)$, and two identical diodes as shown in the figure. The resistance of each diode under forward biasing condition is $10 \Omega$. The time constant of the circuit is $\alpha \times 10^{-3} \text{ s}$. The value of $\alpha$ is . . . . . . .

Can the potential barrier across a $p-n$ junction be measured by simply connecting a voltmeter across the junction?

Which graph represents the variation of charge density with distance across a $P-N$ junction?