<span>Air pollution is the presence of harmful substances in the earths atmosphere </span>
"<span>The genes for melanin pigmentation remain turned on and prepare more melanin than usual to protect the skin from photo-damage when it is exposed to sunlight for long time" is the actual reason. </span>
Answer:
a. 0.5 grams b. 0.25
Explanation:
Just use the half-life formula(I linked it below)
a. 4(1/2)^90/30=1/2
b. 4(1/2)^120/30=1/4