Question

state Ohm's law and write the condition in which this law is obeyed?

Answer 1

electric current flowing through a conductor is directly proportional to the potential difference applied across its ends, providing the physical condition (such as temperature)remain unchanged
hope it's clear to you

Answer 2

ohm's law states that ,
At  a constant temperature the potential difference across the ends of a conducter is directly proportional to the current.
  V directly proportional to I
 V = RI
here R is the constant of proportionality called resistence.
the ohms law  is not applicable for non ohmic metals like semiconducter diode, electrolitic solution etc
the resistence changes if the temperature varies.