Let us understand antidepressants with the example of Noradrenaline before answering the question.

ANTIDEPRESSANTS: Noradrenaline acts as neuro-transmitters and play a role in mood changes. Low level of noradrenaline leads to low signal-sending activity and hence leading to depression. So basically, if a person has low level of noradrenaline, he/she may suffer from depression.

Therefore, under such situation antidepressant drugs are required.

Antidepressant drugs inhibit enzymes which catalyse the degradation of the noradrenaline. Once the enzyme is inhibited, then noradrenaline is slowly metabolized and activates its receptors for longer periods of time, thereby counterbalance the effect of depression.

Hence, antidepressants can be described as the drugs which come inhibits the enzymes which catalyse the degradation of the noradrenaline.

Options (i) Iproniazid and (ii) Phenelzine are the antidepressants drugs

Whereas (iii) Equanil is a tranquilizer which is used in controlling depression and hypertension. (controls depression but isn’t an antidepressant).

And (iv) Salvarsan is a type of antibiotic.

Hence, options (i) and (ii) are correct and options (iii) and (iv) incorrect.