Answer and Explanation:
It's very important to assume that the rate of radioactive decay will remain constant over time to make scientists' lives easier when calculating the ages of fossils, compounds, etc.
If the rate changes, it would be extremely challenging for people to figure out the relative ages of rock strata, fossils, or other substances with radioactive elements in them. This is a fundamental assumption in order to be able to use radioactive dating.
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When an ion loses electrons, it becomes a positive ion even though it does not lose protons. If there are more protons than electrons in the ion, the ion will have a positive charge.
The change of state that has been given in the question is called sublimation. It is actually the process in which a solid gets directly converted to gas without changing into liquid. I hope that this is the answer that you were looking for and the answer has actually come to your desired help.
The answer is A, because of the chemical reaction taking place color can change (as in this case). Hope it helps!