The atomic number of krypton (kr) is 36, and its mass number is 84. how many neutrons does it have?

48 neutrons

Explanation:

Mass number is defined as the sum of number of protons and neutrons that are present in an atom.

Mass number = Number of protons + Number of neutrons

Atomic number is defined as the number of protons or number of electrons that are present in an atom.

Atomic number = Number of electrons = Number of protons

Given:  Atomic number of Krypton = Number of electrons = Number of protons = 36

Mass number of krypton = Number of protons + Number of neutrons  = 84

Thus, 84= 36 + Number of neutrons

Number of neutrons = 48

Thus krypton has 48 neutrons.

altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).