How many moles of argon are present if there are 1.23 x 10^20 atoms?

2.04×10⁻⁴ moles of Ar

Explanation:

We begin from this knowledge:

1 mol of substance has 6.02×10²³ particles

Let's solve this by a rule of three:

6.02×10²³ atoms are contained in 1 mol of Ar

1.23×10²⁰ atoms must be contained in (1.23×10²⁰ . 1) / 6.02×10²³ =

2.04×10⁻⁴ moles of Ar

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