Commonly used route of administration for general anaesthesia is –
This question is a bit confusing one because of the following two facts :-

"For the induction of anaesthesia, intravenous anaesthetics are used mostly".
"For the maintenance of anaesthesia, inhalational agents are used most commonly".

But following statement will clear the doubts.

"Now a day, most of the minor surgical procedures like incision & drainage are done in total intravenous anaesthesia in which intravenous anaesthetics are used for both induction as well as maintenance of anaesthesia".

So,


For major surgical procedure → i) Induction by intravenous anaesthesia, and ii) Maintenance by inhalational anaesthesia.
For minor surgical procedure → Induction and maintenance both by intravenous anaesthesia.
Inhalational
Intravenous
Intra-arterial
Subcutaneous