Suppose the half-life of an element is 10 years. how many half-lives will it take before only about 6% of the original sample remains? 3 half-lives 4 half-lives 5 half-lives 6 half-lives

We can solve this problem by using the equation as shown: A=Aoe^-(ln2/t)T where A is the final amount (0.06 gram), Ao is the initial amount (1g *assumed), t is the half-life (10 years ) and lastly T time elapsed (required). Plug in the values in the equation and you should get  40.5 years and this is approximately 4 half-lives.

According to my calculations I got around 4 half lives

Yes it would be a physical change.