1. The problem is to simplify the expression $-25^{1/2}$. 2. The exponent $1/2$ means the square root, so $25^{1/2} = \sqrt{25}$. 3. Calculate the square root: $\sqrt{25} = 5$. 4. The negative sign in front means we take the negative of the square root, so the expression becomes $-5$. 5. Therefore, the simplified form of $-25^{1/2}$ is $-5$.