remember
(ab)/(cd)=(a/c)(b/d)
and

1kg=1000g=1*10^3g
hmm, I estimate, 4 of them
x=number of attoms
mass of 1 times x=1*10^3
3.95*10^-22 times x=1*10^3
divide both sides by 3.95*10^-22
x=

=

=

a million has 9 zeroes
so 24 zeroes is alot that is a
septillion, so there are 2.5316 septillion uranium atoms in 1kg
a. 4
b. underestimate