Question

How many electrons are there in a neutral atom of $Kr-85$?

Answer 1

Hint:
i) The nucleus of an element contains protons and neutrons, and the electrons are present in the orbitals which are present around the nucleus.
ii) In case of a neutral isotope, the number of positive and negative charged species should be equal, meaning the protons and electrons should have equal numbers.

Complete step-by-step answer:
Krypton is a type of noble gas or also called inert gas which is considerably odourless, colourless as well as tasteless. This gas is present in the atmosphere in trace amounts meaning, very less amount of this gas is found in the atmosphere, nearly around $1ppm$ or parts per million. It is generally used in fluorescent lamps. The concentration of krypton is different in various planets, for instance, the concentration of krypton is observed to be around $0.3ppm$ in mars.

Some of the characteristics of krypton which makes it easily identifiable are the sharp emission of the spectral lines. It can be obtained as a product of the reaction involving fission of metallic elements. Krypton, similar to all other noble gases, has a significant application in photography and lighting. The light emitted by the krypton has many spectral lines which is useful and bright.

The atomic number of krypton is $36$, which means that the element would have $36$ protons in the nucleus of krypton. Now, in the given question we will consider an isotope of this krypton which is $Kr-85$, so it will have $49$ neutrons, as $85-36=49$.

Since the element has $36$ protons, the number of electrons would also be equal, as it is mentioned in the question that the atom is neutral in charge. So, the correct answer would be $36$ electrons.

Note:
i) A neutral atom of $Kr-85$ isotope contains $36$ electrons, as the number of protons are equal in the nucleus of this isotope.
ii) The content of isotope $Kr-85$ present in the atmosphere is exploited in order to find out the facilities of nuclear fuel processing in some countries.