Which of the following statements with regard to the phenomenon of the primary rainbow formation by water droplets is/are correct?

1. It involves refraction and one internal reflection of sunlight.

2. It involves refraction of sunlight only.

3. It is formed as the inner bow.

4. It may involve more than one internal reflection as well as refraction of sunlight.

Select the answer using the code given below :

Which one of the following scientists mentioned that an electron in an atom could revolve in certain stable orbits without the emission of radiant energy?

LIGO experiment confirmed one of the predictions of :

A block of mass 2 kg, moving with the initial speed of 3 m/s comes to rest on a rough horizontal surface after travelling a distance of 3 m. The magnitude of the frictional force is :