How many protons are present in the isotope lithium-7?

• A. 7
• B. 3
• C. 1
• D. 4

Answer: (B)

Verified step by step guidance

1. Identify the element in question, which is lithium. The number of protons in an element is equal to its atomic number.
2. Recall that the atomic number of lithium (Li) is 3, meaning every lithium atom has 3 protons regardless of the isotope.
3. Understand that the isotope notation lithium-7 indicates the mass number (sum of protons and neutrons) is 7, but this does not affect the number of protons.
4. Therefore, the number of protons in lithium-7 is the same as the atomic number of lithium, which is 3.
5. Conclude that the isotope lithium-7 contains 3 protons.