To solve this question, the user needs to know the basics of algebraic equations and the concept of squares.
Let's assume that the negative integer is represented by the variable x. The sum of the square of a negative integer and itself can be represented by the equation:
$x^2 + x = 0$
We can factor out x from this equation:
$x(x + 1) = 0$
Thus, either x = 0 or x + 1 = 0.
If x = 0, then $x^2 + x = 0^2 + 0 = 0$, which satisfies the given condition.
If x + 1 = 0, then x = -1, and $x^2 + x = (-1)^2 + (-1) = 1 - 1 = 0$, which also satisfies the given condition.
Therefore, the answer is either A (-1) or C (0), as these are the values of x that satisfy the equation.
Option A (-1) and Option C (0) are both correct answers because the equation is satisfied by both values of x.
Option B (-2) is incorrect because this value does not satisfy the equation.
Option D (-1/2) is incorrect because it is not an integer and it does not satisfy the equation.
The Answer is: A or C