What are the conditions under which $Ohm's$ law is not obeyed?

(N/A) $Ohm's$ law is not obeyed under the following conditions:
$(i)$ The relationship between potential difference $(V)$ and current $(I)$ is non-linear.
$(ii)$ For a given value of $V$,there is more than one value of $I$ (i.e.,the relation is non-unique).
$(iii)$ The relationship between $V$ and $I$ depends on the sign of $V$ (i.e.,if the direction of current is reversed,the magnitude of current for the same potential difference changes).