Ohm's law fails in

Two $PN$-junctions can be connected in series by three different methods as shown in the figure. If the potential difference across the junctions is the same,then the correct connections will be:

In the given figure,each diode has a forward bias resistance of $30\, \Omega$ and infinite resistance in reverse bias. The current ${I}_{1}$ will be $....\,A$.

When a forward bias is applied to a $p-n$ junction,it . . . . . . .

Which of the following circuits represents a forward biased diode? Choose the correct answer from the options given below.

$A$ $5 \, V$ battery is connected across the points $X$ and $Y$. Assume $D_{1}$ and $D_{2}$ to be normal silicon diodes. Find the current (in $A$) supplied by the battery if the positive terminal of the battery is connected to point $X$.