Final answer:
The correct expression that matches the description of a monomial of the second degree with a leading coefficient of 3 is 3n^2, which corresponds to Choose C.
Step-by-step explanation:
The question requires us to pick the expression that is a monomial of the second degree with a leading coefficient of 3. We are given four options to choose from.
A monomial is an algebraic expression with only one term, and the degree of a monomial is the sum of the exponents of all its variables. The leading coefficient is the coefficient of the term with the highest degree when the polynomial is written in standard form, which means the terms are ordered from highest to lowest degree.
Given the description, we are looking for an expression that is a single term (monomial) with a variable raised to the power of 2 (second degree), and the coefficient of that term should be 3. Therefore, the correct expression is 3n^2 as it is the only option that fits all these criteria. This matches with Choice C: 3n^2.