Correct Answer  Option 3 : decrease by 87.5%
The correct answer is option 3) i.e. decrease by 87.5%
CONCEPT:

Kepler's laws of planetary motion
 The first law (Law of orbits): All the planets revolve around the sun in elliptical orbits having the sun at one of the foci.
 The second law (Law of areas): The radius vector drawn from the sun to the planet sweeps out equal areas in equal intervals of time.
 The third law (Law of periods): The square of the time period of revolution of a planet around the sun in an elliptical orbit is directly proportional to the cube of its semimajor axis.
CALCULATION:
From the third law of Kepler, the square of the time period (T) is directly proportional to the cube of the semimajor axis (R).
⇒ T2 ∝ R3
Let the radius and time period of Earth be R and T respectively.
If R' and T' are the new radius and time period,
When the radius of Earth's orbit is reduced by 75%, R' = 25% of R = 0.25 R
Then the new time period will be:
\(\Rightarrow( \frac{T'}{T} )^2= (\frac {R'}{R})^3\)
\(\Rightarrow( \frac{T'}{T} )^2= (\frac {0.25R}{ R})^3\)
\(\Rightarrow( \frac{T'}{T} )^2= 0.25^3\)
\(\Rightarrow T' = \sqrt{0.25^3} T= 0.125T\)
\(\Rightarrow T' = 12.5\%T\)
Therefore, the new time period gets decreased by 87.5% (100%  12.5% = 87.5%)