The condition for achieving laser action are(i) The system must be in a state of population inversion(ii) The excited state of the system should be in metastable state(iii) The atom should be in lower energy state(iv) No conditions required

The correct condition for achieving laser action is:

(i) The system must be in a state of population inversion.

Population inversion is a crucial requirement for laser action. In a laser, more atoms or molecules are in higher energy states (excited states) than in lower energy states (ground states), which is the opposite of what occurs in thermal equilibrium. This population inversion allows for stimulated emission to dominate over absorption, leading to the amplification of light through the laser medium.

The other conditions mentioned in options (ii), (iii), and (iv) are not necessary for achieving laser action. While metastable states can be beneficial in some laser systems, they are not a strict requirement for all lasers. The atom being in a lower energy state is not a condition because population inversion means there are more particles in higher energy states. Option (iv) is incorrect because conditions are indeed required for laser action, and population inversion is a fundamental condition.