Question

What are the number of protons, neutrons, and electrons for the −2 anion from the 17O isotope of oxygen? (The atomic number of oxygen is 8.)
Select one:
a. 8p+; 8n; 6e−
b. 8p+; 10n; 8e−
c. 7p+; 10n; 10e−
d. 8p+; 9n; 10e−

Answer 1

The correct answer is d. 8p+; 9n; 10e−

Oxygen exists in three isotopes ¹⁶O, ¹⁷O and ¹⁸O. The atomic number of oxygen is 8. It means its nuclei has 8 protons. The given is oxide⁻² anion. This means it has gained 2 electrons. Thus, oxide anion have 8 protons and 10 (8+2) electrons. The number of neutrons depends on the isotope, in this question mass number is given¹⁷O. The mass number is the sum of the protons and neutrons in the nucleus. Hence, number of neutrons oxide anion will be 17-8 = 9 neutrons.