The correct option is C 45×10−8cm2
Let d be the diameter of steel wire and L be the length of wire.
So, Poisson ratio (ν)=0.3=ΔddΔLL
Now, Stress (σ)=FA=150.05×10−4=300×104 N/m2
Young's modulus (Y)=σΔLL
⇒ΔLL=σY=300×1042×1011=1.5×10−5
Now, ν=ΔddΔLL=Δdd1.5×10−5
⇒0.3=Δdd1.5×10−5
⇒Δdd=0.3×1.5×10−5=0.45×10−5
Now, ΔAA=2Δdd=0.9×10−5
⇒ΔA=0.9×10−5×A=0.9×0.05×10−5=0.045×10−5 m2
⇒ΔA=45×10−8cm2