A jar contains several different types of atoms. The proportions of these atoms can be changed slightly without changing any substance in the jar. This jar contains

a mixture

Explanation: A mixture consists of different atoms that are not chemically bonded. It is of two types of the heterogeneous mixture and homogeneous mixture. The chemical substances can be differentiated visually in the heterogeneous mixture.

In a mixture, the proportion of atoms can be slightly changed without changing or modifying any substance. This is because the individual substances in mixture keep their properties when mixed together. Further, mixtures have variable compositions and substances. these mixtures can be are separated using physical methods.

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

that scientist would be robert hooke