The correct option is C <30 cm
Given that,
Metallic tape gives correct value at 25∘C.
At 10∘C, the length of the metallic tape is 30 cm.
From the concept of linear expansion, we know that
Change in length of the tape with change in temperature ΔT
=ΔL=L0(αΔT)
As the temperature decreases, tape will decrease in its length.
So, the reading 30 cm measured on the tape is lesser than the actual length of the wooden piece.
Hence, option (c) is the correct answer.