Answer:
the answer is A
Explanation:
physical changes does not change the property of matter.
In order of reactivity: magnesium, iron, copper, silver
The speed and wavelength changes as a waves travels to a different depth. Slower and bigger amplitudes in shallower depths. Freq does not change
<u>Answer: </u>
A sample initially contained 150 mg of radon-222. After 11.4 days only 18.75mg of the radon-222 in the sample remained where 3 half-lives have passed
<u>Explanation:</u>
Given, the initial value of the sample,
= 150mg
Final value of the sample or the quantity left, A = 18.75mg
Time = 11.4 days
The amount left after first half life will be ½.
The number of half-life is calculated by the formula

where N is the no. of half life
Substituting the values,


On equating, we get, N = 3
Therefore, 3 half-lives have passed.