Answer:
a) Radius decreases
Step-by-step explanation:
Resistance of any conductor is directly proportional to the length of the conductor and inversely proportional to its cross-sectional area.
So, in mathematical terms, the resistance is written as
= ρ

As we know, cross sectional area is related to the radius of the conductor so if the radius of the conductor is decreased, the cross-sectional area will also decrease.
And if the cross-sectional area will decrease, the resistance will increase.
Thus decreasing the radius, increases the resistance.