The length of a certain wire is kept same while its radius is doubled. how will the new resistivity of this wire change? -g

The resistivity of the wire will not change: in fact, the resistivity is a property of the material used to build the wire, so it does not depend on its length.

Instead, the resistance of the wire depends on the length L:

where  is the resistivity of the material and A is the cross-sectional area of the wire.