The correct option is C 1.6π×10−4 J
Given,
Radius of soap bubble, R=2.1 cm=2.1×10−2 m
Surface Tension, T=4.5×10−2 N/m
We know that, number of free surfaces for soap bubble, n=2
Surface energy = Surface tension × surface area × number of free surfaces
⇒E=T×A×n
=4.5×10−2×4π(2.1×10−2)2×2
[ surface area =4πR2 ]
=1.6π×10−4 J