Atom X contains seven protons and seven neutrons. atom Z contains seven protons and eight neutrons. which of the following statements correctly describes the two atoms? A. they are isotopes.
B. they are radioactive.
C they have the same mass number.
D they are atoms of different elements.

The correct answer is option A: they are isotopes.

Explanation:

From atom X we know that the number of protons is 7 and the number of neutrons is 7 and from atom Z we know that the number of protons is 7 and the number of neutrons is 8.

Since the number of protons of atom X and atom Z is the same, we have that atom X and atom Z is the same element. The difference in the number of neutrons tells us that atom X and atom Z are isotopes. Remember that an isotope is one element that has atoms with different numbers of neutrons.            

The mass number is given by:              

Where n is the number of neutrons and p is the number of protons.

For atom X and atom Z we have:

Hence, they have a different mass number.  

We know that the element with 7 protons is nitrogen. The first isotope is and the second isotope is . Both isotopes are stables (they are not radioactive).  

Therefore, the correct answer is option A: they are isotopes.

I hope it helps you!                                                          

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg