How much of a 24-gram sample of Radium-226 will remain unchanged at the end of three half-life periods?

Which of these best describes an ionic bond?

You encounter a solution that is acidic and you decide to test it by adding a small amount of a strong acid. the ph lowers slightly but is approximately unchanged, and still remains acidic. what can you say about the solution? a. it is a buffer solution. b. it is not a buffer solution it is a strong acid solution. d. the solution has been neutralized. e. the solution has excess acid present

Can someone me with 3 and 4 plz. this is for masteries test.