Answer:
A
Explanation:
The total number of each type of atom always stay the same.
<span>The option A is correct answer. The isotopes are X and Y. The isotopes are those which have same atomic number but different mass number. Since atomic number has same number of protons or electrons. Thus, isotopes have same number of protons or electrons. Therefore, X and Y are isotopes.</span>
Answer:
the frequency of light is

Explanation:
from v = λf
speed of light in air, v = 3.0*10^8ms^-1