The gravitational force depends on the masses of the two objects and the distance between them, according to Newton's law of universal gravitation:
\[ F = \frac{G \cdot m_1 \cdot m_2}{r^2} \]
where \( F \) is the gravitational force, \( G \) is the gravitational constant, \( m_1 \) and \( m_2 \) are the masses of the two objects, and \( r \) is the distance between their centers.
If the mass of one object decreases by one-half while the mass of the second object remains the same, the gravitational force will also decrease by one-half. This is because the force is directly proportional to the mass of the objects involved.
Therefore, the correct response is:
The gravitational force decreases by one-half.