Question

Old resistance of wire is one om if length is doubled what will be the new resistance

Answer 1

It would be 4 ohm after the length is doubled

Answer 2

Resistance = Resistivity*length/area

Here we note that the resistance is directly proportional to length and inversely proportional to area of cross section ....  

Now a/c to question,;

Length of wire is double then area is reduced to half...

Now  

New resistance = resistivity*2length/area/2

New resistance =(resistivity*length/area)*4

New resistance = 4rohm