Explanation :
According to Newton's gravitational law, the gravitational force depends directly on the product of the masses and the inversely proportional to the square of the distance between them.
Mathematically,

G is the gravitational constant
are the masses
r is the distance between the masses.
When the mass of the sun is reduced to 75,000, the gravitational force would decrease (due to direct relation between the mass and the force). As a result, the orbit gets larger.
So, the correct option is (c) "The orbit gets larger".