Which two statements are true about a system?
a) all systems are made by humans
b) a system is a group of objects analyzed as one unit
c) energy they moves across system boundaries is conserved
d) there’s only one way to define the boundaries of a system

The correct answers are B and C. A system is a group of objects analyzed as one unit, and energy that moves across system boundaries is conserved.

Explanation:

A system is "a complex object whose parts or components are related to at least some of the other components", it can be material or conceptual. All systems have composition, structure and environment, but only material systems have mechanisms (or processes), and only some material systems have shape (form).

According to systemism, all objects are systems or components of another system. For example, an atomic nucleus is a physical material system composed of protons and neutrons related by strong nuclear interaction; a molecule is a chemical material system composed of atoms related by chemical bonds; a cell is a biological material system composed of related organelles by non-covalent chemical bonds and metabolic pathways; a cerebral cortex is a biological material system composed of neurons related by action potentials and neurotransmitters; an army is a social and partially artificial material system composed of people and related artifacts by command, supply, communication and war; and a scientific theory is a logical conceptual system composed of hypotheses, definitions, and theorems related by correlation and deduction.

answer: c. the experiment shows that the red substance experienced a chemical change.

explanation: chemical change is the change in which chemical composition of the substance changes. physical change is the change in which there is no change in chemical composition.

chemical changes are accompanied by following changes:

a) precipitate formation

b) energy is released or absorbed

c) formation of bubbles

d) change in color

as it is given that the red color has disappeared and there is production of gas, it means the red substance has undergone a chemical change.

e