Correct spelling, explanation: necessary comes from the noun necessity (which is used for saying about things that must be done). The correct spelling includes one c, so neccessary is an incorrect form.

Definition of necessary:
adjective, something that is crucial/ that needs to be done in order to achieve a particular goal, effect. It can also be used in a negative, to show disapproval about something.
Was it really necessary to remind her about the past? She is totally different person right now.
It is really unnecessary to stay longer in the office today.

Idioms and phrases with necessary:
→ necessary evil, the situation where we have to do something and accept it, even if we know it is morally wrong, usually for the sake of something important: Nobody likes paying taxes, but it is a kind of necessary evil
→ deem it necessary, to say that something is crucial: Jack deemed it necessary to buy a new car, while Mary wanted to recondition the bedroom.
→ the necessary, casual way to say money or any kind of income (what is interesting, it is also an old term meaning toilet or bathroom): Don’t worry about my bills, I can always use more of the necessary.

Incorrect spelling, explanation: the word is the combination of a noun necessity and a suffix -ary, which general meaning, in addition to creating an adjective, is connected to. It is therefore mistaken to add one more c in the middle of the word and necessary is the only correct spelling.

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling