This question tests the historical Thomson model of the atom, proposed by J. J. Thomson in 1904 shortly after his discovery of the electron. Because atoms are electrically neutral overall, Thomson needed a picture in which negatively charged electrons were balanced by an equal amount of positive charge.

His model — popularly called the Plum Pudding Model (and also likened to seeds embedded in a watermelon) — proposed that:

• The atom is a sphere of uniformly distributed positive charge, spread throughout the atom's volume.
• The tiny, negatively charged electrons are embedded within this positive sphere, like plums in a pudding or seeds in a watermelon, arranged so that the total negative charge cancels the total positive charge.

This matches the option describing electrons embedded in a positively charged sphere like seeds in a watermelon, which is therefore correct.

The other options describe later or simply incorrect pictures:

• Electrons moving in fixed orbits around the nucleus is the Rutherford/Bohr nuclear picture (1911/1913), which came after Thomson and, importantly, requires a central nucleus that Thomson's model does not have.
• Electrons orbiting around neutrons in elliptical paths is wrong on two counts: the neutron was not even discovered until 1932, and no atomic model places electrons in orbit around neutrons.
• Electrons randomly placed inside the nucleus is incorrect because Thomson's model has no dense nucleus at all; the positive charge is spread out, not concentrated.

Thomson's model was ultimately overturned by Rutherford's gold-foil alpha-scattering experiment, which showed the positive charge and mass are concentrated in a tiny central nucleus.