4. thorium-234 has a half-life of 24.1 days. what percentage of the original thorium-234 in a sample will remain after 144.6 days?

How many half lives have elapsed?
actually the formula is like this
A=P(1/2)^(t/h)
P=iniital amount
t=time
h=half life
A=final amount
so

hmm, percent
so P=1 then
A=1(1/2)^(144.6/24.1)
A=1(1/2)^6
A=1/64
A=0.05625
so 5.625% is left

Answer) by studying proton collisions hope this : )

The problem here is that according to aufbau principle before 3d orbital 4s subshell comes.after filling 3p orbital with electrons you have 4 electrons left, you place two in 4s with opposite spin and the other two in 3d in any of its two orbitals of total five orbitals with the same spin.