Prior to its discovery on earth, helium was first detected in the sun. explain how this can be possible.

Helium is not that common on earth, it does not react with other elements, and scientists didn't know that it should exist and so they weren't looking for it on earth. The element that created the lines they found in the sun's spectrum in 1868 was believed to be a new element and was  named helium (from the Greek ''Helios'' meaning sun) and when they finally knew it existed they found it on earth.

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Hi; /c

Answer : option a) 84explanation :

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.