Passage IV
Atomic nuclei can be represented by the combination of symbols
where Z is the number of protons in a nucleus of Element X, and A (equal to Z plus the number of neutrons) is the mass number of the same nucleus. For example, 
represents a nucleus of carbon containing 6 protons and 6 neutrons;
represents a nucleus of a different isotope (type) of carbon that contains 6 protons and 8 neutrons.
Atomic nuclei undergo 3 types of radioactive decay. Particles emitted during the 3 types of decay are listed in Table 1. Figure 1 shows a sequence of radioactive decays, called the uranium series, that begins with the decay of 
.
19. How many neutrons, if any, does a nucleus of the isotope of helium listed in Table 1 contain?
Your Answer is
Correct Answer is C
Explanation
In Table 1, 42The 4 in the upper left corner of He represents the proton and neutron The sum of the numbers, and the 2 in the lower right corner represents the number of protons, so the number of neutrons is equal to 4-2=2