What experimental evidence led Rutherford to conclude the following: (a) The nucleus of the atom contains most of the atomic mass. The nucleus of the atom contains most of the mass since only a collision with a very dense, massive object would cause an alpha particle to be the source. (b) The nucleus of the atom is positively charged. The positive alpha particles their initial flight indicating that the nucleus of the atom is also positively charged. (c) The atom consists of mostly empty space. Most alpha particles pass through the gold foil leading to the conclusion that the atom is mostly empty space.

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Explanation:

The experiment of Ernest Rutherford involved the bombardment of a thin gold foil with alpha particles from a radioactive source. A zinc sulphide screen was used to follow the movement of the alpha particles.

It was discovered that most of the alpha particles  followed a  straight path through the gold foil. Some of them were scattered through large angles and few were even scattered in the backward direction.

Since alpha particles were heavier than electrons, they must have been deflected by very strong forces.

These experimental evidences led to the conclusions stated in the question.

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.

the awnser is group 12