Please help, I need help with this test question

I believe this is right-

for the first question, it should be fluffy

and for the second it should be spot

potential energy is unused

kinetic energy is being used

proof in explanation

Explanation:

First, we will calculate the number of half-lives:

where,

n = no. of half-lives = ?

t = total time passed = 2100 million years

= half-life = 700 million years

Therefore,

Now, we will calculate the number of uranium nuclei left ():

and the rest of the uranium nuclei will become thorium nuclei ()

dividing both:

Hence, it is proven that after 2100 million years there are seven times more thorium nuclei than uranium nuclei in the rock.