Answers (1)
Active: somebody does something
Passive: something is done - (by whom may or may not be emphasized)
"Avoid using the passive voice." - active - subject: you (imperative) - verb: avoid
"Use of the passive voice is to be avoided." - passive - subject: use or using (gerund) - verb: some form of to be
Active: "What do you want?"
Passive: "What is wanted?"
Because the new verb "wanted is assumed singular. If you meant what (things) are wanted, then it would be plural.
But why you have used "is" verb, why not "are".