To multiply the fractions \(-\frac{2}{5}\) and \(\frac{3}{10}\), we multiply the numerators and denominators:
\[ \frac{-2 \times 3}{5 \times 10} = \frac{-6}{50} \]
Now, we need to simplify \(-\frac{6}{50}\). We can do this by finding the greatest common divisor (GCD) of the numerator and denominator, which is 2:
\[ -\frac{6 \div 2}{50 \div 2} = -\frac{3}{25} \]
Thus, the answer in simplest form is \(-\frac{3}{25}\). Therefore, the correct option is:
-3/25