Answer :

GinnyAnswer
To answer this question, we need to know two key pieces of information about an atom: its atomic number and its mass number. Lithium (Li) has an atomic number of 3. The atomic number tells us the number of protons in the nucleus of an atom. Since the number of protons determines the element, every lithium atom will have 3 protons. The mass number of an atom is the sum of protons and neutrons in the nucleus. The most common isotope of lithium is lithium-7. The "7" in lithium-7 is the mass number. This indicates that the sum of protons and neutrons in the nucleus equals 7. To find the number of neutrons, we subtract the atomic number (number of protons) from the mass number. Thus: Number of neutrons in lithium = Mass number – Atomic number Number of neutrons in lithium = 7 – 3 Number of neutrons in lithium = 4 Therefore, the correct answer is: C. 4
Lithium (Li) is an element with atomic number 3. The atomic number of an element represents the number of protons in the nucleus of an atom. To find the number of neutrons in an atom of lithium, we need to subtract the atomic number from the mass number.

The atomic mass of lithium is approximately 6.94 u (atomic mass units). Since the atomic number is 3, we can conclude that lithium has about 4 neutrons:

Number of neutrons = Atomic mass number - Atomic number
Number of neutrons = 6.94 - 3
Number of neutrons ≈ 3.94

Since the number of neutrons must be a whole number, and lithium typically has 4 neutrons.

Therefore, the correct answer is:

C. 4