What chemical is a letter or pair of letters representing an element?

Atomic Oribal

Explanation:

There are four basic types of electron orbitals – s, p, d, and f. (Visual representations can be found in the tutorial above.) The s subshell is a spherical orbital which can contain up to two electrons. Each energy level has one s subshell.

the mass of the cathode increases because ions from the solution get reduced to atoms and become part of the cathode.

explanation:

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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.