A piece of iron is heated in a flame. It first becomes dull

A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using

1. Wien’s displacement law
2. Kirchoff’s law
3. Newton’s law of cooling
4. Stefan’s law

Wein’s displacement law
According to this law
λ_max ∝ 1/T
or, λ_max × T = constant
So, as the temperature increases λ decreases.