What is true if a liquid and a gas are in equilibrium? A. Liquid molecules forming a gas and gas molecules forming a
liquid are equal in number.
B. The number of liquid molecules and the number of gas molecules
vary
C. Liquid molecules are continually forming to replace escaping gas
molecules.
D. The liquid molecules stay liquid, and the gas molecules stay gas.

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considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.