Which of the following does not show mutarotation?

The synthesis of crotonaldehyde from acetaldehyde is an example of $.......$ reaction.

If the magnitude of average speed and average velocity over an interval of time are the same,then:

It takes $10$ minutes to cool a liquid from $61^oC$ to $59^oC$. If room temperature is $30^oC$,then the time taken in cooling from $51^oC$ to $49^oC$ is ....... $\min$.

The lanthanide contraction is responsible for the fact that

An electromagnetic wave of intensity $1400 ~W/m^2$ falls on a metal surface of area $1.5 ~m^2$ and is completely absorbed by it. Find the force exerted by the beam.