Needing physics assistance please?

Question

1. Which equation below would you use to determine the number of neutrons in a given nucleus when you are given the atomic number (Z) and atomic mass (A)?

a. N = A + Z

b. N = A/Z

c. N = AZ

d. N = A – Z

A gas is collected from a radioactive material; upon inspection, the gas is identified as helium. The presence of the helium indicates the radioactive sample is most likely decaying by?

a. Alpha

b. Beta+

c. Beta-

d. Gamma

3. Use the following Half-life Graph to answer the following question: http://i10.photobucket.com/albums/a141/Skeevald/7_testhalflife.gif

When you are left with 6.25 kg of the radio active isotope, how many half-lives have occurred from time equals zero?

a. 1

b. 3

c. 6

d. 12

4. How many neutrons does the following isotope of Nitrogen have? 15 / 7 N

5. 214/84 Po --> 210/82 Pb + 4/2 He is an example of...?

a. alpha decay.

b. beta decay.

c. gamma decay.

d. half-life decay

Thanks a lot!

Answer 1

1. D. Atomic mass is the number of protons(atomic number) + neutrons.

2. A, Alpha. Alpha means that the substance emits Helium atoms (2 protons and 2 neutrons).

3. C. It's right there on the graph. 50 at time 0, 25 at time 1, 12.5 at time 2, 6.25 at time 3

4. Again, neutrons are Mass-number, so 15-7=8

5. A. Again, Losing 2 protons and 2 neutrons is alpha decay (helium emission).