Correct Answer - Option 3 : 113 mm

__Concept:__

In a tension test on a bar, gauge length means the length over which extension is measured.

\(GL = 5.65\;\sqrt {{A_o}}\)

Where Ao = Initial cross-sectional area before loading

Gauge length is independent of the length of a bar, material of bar, and shape of cross-section.

__Calculation:__

Given,

A_{o} = 50 × 8

\({\rm{Guage\;length}} = 5.65\;\sqrt {50 × 8} = 113\;{\rm{mm}}\)