An atom with a mass number of 61 amu has 33 neutrons in its nucleus.
What element is this ?

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Explanation:

amu = atomic mass unit

If the amu is 61, and we have 33 neutrons, then there are 61-33 = 28 protons. The number of protons directly determines the element. Use the periodic table to find that the element Nickel (symbol "Ni") has 28 protons. The number up top shows the number of protons. For some periodic tables, the number down below (some decimal value) represents the atomic mass. This is usually the average atomic mass when considering all varieties of isotopes.

Nickel is a transition metal found in the middle portion of the periodic table, in the top-most row. It has Cobalt (Co) on the left side, Copper (Cu) on the right side, and Palladium (Pd) below it. See the diagram below.

wavelength variability is the right one