The first nucleus of an atom was shown as?
a. a solid mass
b. a fuzzy cloud
c . a mass of protons and neutrons
d. a mass of protons

The first atomic model was the one proposed by Jhon Dalton, according to which it is postulated that:

"Matter is made up of indivisible, indestructible and extremely small particles called atoms."

That is, the atom is a solid and indivisible mass.

However, over time some limitations were found in Dalton's atomic model and was replaced by the Thomson's atomic model, then by Rutherford's, Bohr's, Sommerfield's, and finally Shrodinger's.

Currently it is known that each atom is composed of a nucleus and one or more electrons attached to the nucleus, which is composed of one or more protons and typically a similar number of neutrons.

In addition, the atomic nucleus is the central part of the atom and concentrates most of the total mass of the atom.

Therefore, the correct option is A.

real, smaller and upside-down.   so the answer should be b.