Which contribution is a modification to Thomson's plum pudding model? Atoms are indivisible.
Electrons are scattered in an atom.
A positively charged nucleus sits at the center of an atom.
Atoms of the same element have the same properties.

Option C: A positively charged nucleus sits at the center of an atom.

Explanation:

Thompson’s plum pudding model was a model proposed by Thompson to show that an atom consisted of more than one fundamental unit.

In Thompson's model, he suggested that the atom consisted of a cloud of positive charges which were surrounded by electrons which are negative charges distributed throughout.

Now, Thompson's experiment was later rejected by Ernest Rutherford when he carried out the gold foil experiment and came to the conclusion where he proposed a model that the atom consisted of mainly empty space and that all its positive charge are concentrated at its center and further surrounded by a cloud of electrons.

From the given options, the correct one is Option C.

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the maximum mass of nh3 is nh3 in grams