Uranium-238 decays to Lead-206. Both Rock X and Rock Y initially had a ratio of 100%. Uranium-238 to 0% Lead-206. Today, Rock X has a ratio of 50%. Uranium-238 to 50% Lead-206. Rock Y has a ratio of 25% Uranium-238 to 75% Lead-206. Which rock is older?

Rock Y

Explanation:

The rock that is older shall be determined based on the number of half lives it has witnessed. A half life is simply the amount of time required for a sample to decay to half of its original mass.

Rock X

From 100% uranium, it decays to 50% uranium.  This means it went through just one half life.

Rock Y

From 100% uranium to 25% uranium

100 --> 50 (first half life)

50 --> 25 (second half life)

This means it wen through 2 half lives.

Rock Y is older than Rock X

explanation:

since this is put under health, i would define "ethical (medical) behavior" the way the oath for doctors is recited.   "first do no harm."

but the term in general means when given a choice between right and wrong, we should always choose right. if we do, then we are practicing ethical behavior.

i believe it is-

d.) gravity pulled particles of dust and gas together to form planets.