stress in the bar

Question

A free bar of length 1 m is uniformly heated from 0⁰ C to a temperature of t⁰ C. $\alpha$ is the coefficient
of linear expansion and E the modulus of elasticity. The stress in the bar is

(a) $\alpha$ tE                               (b) $\alpha$ tE/2
(c) zero                                     (d) none of the above

Answer 1

Zero will be d answer...as there is no restriction...hence no thermal stress

Answer 2

a- Thermal stress formula

Answer 3

$\therefore$ The stress in the bar is zero