The answer is C because 2, 5, 23, and 29 are prime numbers (you can also look up a chart and highlighted numbers are prime). prime numbers is a whole number greater than 1 and cannot be formed when multiplying two smaller numbers that are whole. it must involve itself in a multiplication equation.
For part (a) the answer is 400 grams for part (b) 198.63 grams and for part (c) 20 years.
<h3>What is exponential decay?</h3>
During exponential decay, a quantity falls slowly at first before rapidly decreasing. The exponential decay formula is used to calculate population decline and can also be used to calculate half-life.
We have an equation for radioactive decay:

a) Plug t = 0

m(0) = 400 grams
b) plug t = 20 years

After solving:
m(20) = 198.63 grams
c) Plug m(t) = m(0)/2 = 400/2 = 200 grams

x = 19.80 years ≈ 20 years
Thus, for part (a) the answer is 400 grams for part (b) 198.63 grams and for part (c) 20 years.
Learn more about the exponential decay here:
brainly.com/question/14355665
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Mark brainliest please
Hope this helps
Answer:
<em>therefore</em><em>,</em><em> </em><em> </em><em>option</em><em> </em><em>B </em><em>is </em><em>correct</em>
<em>hope </em><em>this </em><em>answer </em><em>helps </em><em>you</em><em> </em><em>dear.</em><em>.</em><em>.</em><em>take </em><em>care!</em>