J.J. Thomson’s model of the atom was abandoned because

Step 1: Analyze the question The question asks why J.J. Thomson's "plum-pudding" model of the atom was abandoned. We need the experimental evidence that disproved it.

Step 2: The concept Thomson (1897-1904) proposed that the atom is a sphere of positive charge with electrons embedded in it, like plums in a pudding or seeds in a watermelon. The positive charge was thought to be spread evenly throughout the atom.

Step 3: What disproved it In 1909, Geiger and Marsden, working under Ernest Rutherford, fired alpha particles at a thin gold foil:

• Most alpha particles passed straight through.
• A small number were deflected through large angles.
• A very few (about 1 in 8000) bounced almost straight back.

If Thomson's model were correct, the positive charge would be spread out thinly, and the alpha particles should have passed through with only tiny deflections. Large-angle scattering could not be explained. Rutherford concluded that the positive charge and most of the mass are concentrated in a tiny, dense nucleus, giving the nuclear model of the atom.

Step 4: Check the options

• A. It could not explain the scattering of alpha particles. Correct. This was the key experimental failure.
• B. The neutron was discovered by Chadwick in 1932, long after Thomson's model was already replaced, so this was not the reason.
• C. Thomson's model did give the atom a size, so this is not the reason.
• D. The name "plum-pudding" is just a nickname, not a scientific reason for rejection.
• E. A model is not rejected for lacking similarity to a phenomenon, but because experiments contradict it.

Answer: A

Exam tip: Link names to experiments. Thomson → electron and plum pudding. Rutherford → alpha scattering and nucleus. Bohr → energy levels. Chadwick → neutron. In NECO, JAMB, and WASSCE, "alpha scattering" almost always points to the failure of Thomson's model and the birth of Rutherford's.