A fire work gave bright crimson light. It probably contain an element of

A firework gave bright crimson light. It is probably a salt of:

A fire work gave green light. It probably contained a salt of

A fire work gives out crimson coloured light. It contains the salt of

A is a set containing n elements. A subset P of A is chosen at random. The set A is reconstructed by replacing the elements of P. A subset Q is again chosen at random. The probability that Q contains just one element more than P, is

A is a set containing n elements. A subset P of A is chosen at random. The set A is reconstructed by replacing the elements of P. A subset Q is again chosen at random. The probability that Q contains just one element more than P, is

Rods are sensitive to bright light.

The biprism experiment is performed by using first the blue light of wavelength 4800 Å and then with red light. It is found that the fourth bright band of blue light coincides with the third bright band of red light. What is the wavelength of red light?