<u>Answer:</u> The amount of element X remain after 40 years is 18.75 grams
<u>Explanation:</u>
We are given:
Total time period = 40 years
One half life = 10 years
Calculating the number of half lives,
To calculate the amount of element X after 4 half lives, we use the equation:
where,
a = amount of X after n-half lives
= initial amount of X = 300 g
n = number of half lives = 4
Putting values in above equation, we get:
Hence, the amount of element X remain after 40 years is 18.75 grams