Is it correct to marry for citizenship in USA ?

If you're marrying them for the sole purpose of acquiring citizenship, no, it is not wise. At all. Authorities call that "visa and marriage fraud".

When it comes to immigration, you better marry for love. Because the process takes years to complete, will have a lot of ups and downs and you'll need that support to successfully navigate that process. Very few people have the endurance to go through that process solely for fraudulent purposes. Too easy to slip up and get caught. Most people cannot keep up a lie and keep it straight for 4-6 years the process will entail from entry through marriage through green card to citizenship.

And if you do opt to try for a "marriage of convenience" and somehow manage to get to citizenship, at least in the USA if it is later discovered that you did that for the purposes of obtaining citizenship, you can have that citizenship stripped from you and be deported. It's rare but it does happen. There's also no statute of limitations on it. If it comes out 20 years later you married out of convenience, you can still have your citizenship stripped from you, your spouse, especially if it is a former spouse, prosecuted and you deported for life.