Answer: [tex]A.\ 3n^2[/tex]
Step-by-step explanation:
Monomial is just a kind of polynomial with just one term.
A monomial of 1st degree means the variable should have power of 1. For example : [tex]3x, 4y , 5t...[/tex] etc.
Similarly, A monomial of 2nd degree means the variable should have power of 2. For example : [tex]3x^2, 4y^2 , 5t^2...[/tex] etc.
So, from all the options , the correct option is [tex]A.\ 3n^2[/tex], where the variable has power of 2, i.e. its a monomial of the 2nd degree with a leading coefficient of 3.
Note:
[tex]B.\3n-n^2 \text{ : It is not monomial, as it has 2 terms.}\\C.\3n^2-1 \text{ : It is not monomial, as it has 2 terms.}\\D.\2n^3 \text{ : It is a monomial,but of 3rd degree.}\\[/tex]
