Answer: Manholes are usually round, primarily because roundness is the best shape to resist the compression of the earth; covers are round because they are easier to manufacture than square or rectangular shapes, they are easier to move by rolling, and they can't fall into the opening.
Explanation:
Decay is a type of degradation reaction and thus is considered a first order reaction. thus the formula goes like this.
rate constant= 0.693/half life
so here...
rate constant= 0.693/1620 year^-1
<span>1 Cu + 2 H</span>₂<span>SO</span>₄<span> = 1 CuSO</span>₄<span> + 2 H</span>₂<span>O + 1 SO</span>₂
Coefficient od CuSO₄ = 1
hope this helps!