Introduction:
Resistance is a measure of the opposition to the flow of electric current through a material. The resistance of a wire depends on its length, cross-sectional area, and the material it is made of. In this question, we are asked to determine how the resistance of a wire changes when it is doubled on itself.

Explanation:
When a wire is doubled on itself, its length becomes twice the original length. Assuming the cross-sectional area of the wire remains the same, we can use the following equation to calculate its new resistance:

R2 = (ρ * L2) / A

Where:
R2 = New Resistance
ρ = Resistivity of the Wire Material
L2 = New Length of the Wire
A = Cross-Sectional Area of the Wire

Since we know that the new length of the wire is twice the original length, we can substitute 2L for L2 in the above equation and simplify it as follows:

R2 = (ρ * 2L) / A
= (2ρL) / A
= 2(ρL / A)

Therefore, the new resistance of the wire is twice the original resistance. This means that doubling the length of the wire by folding it on itself results in an increase in resistance by a factor of 2.

Conclusion:
In conclusion, when a wire is doubled on itself, its length becomes twice the original length and its resistance is doubled as well. This is because the resistance of a wire is directly proportional to its length, and doubling the length of the wire doubles its resistance.

The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made.The resistance of a wire can be expressed as R=ρAL​, 
where,
ρ - Resistivity  - the factor in the resistance which takes into account the nature of the material is the resistivity
L - Length of the conductor
A - Area of cross section of the conductor.
From this relation, we observe that the length is directly proportional to the resistance and the area of cross section is inversely proportional to the resistance.
That is, if L becomes 2 L, R becomes 2 R. R′=ρA2L​. So, R = 2R'.
Hence, If the length of a wire is doubled, then its resistance becomes 2 times.