Multiple Choice
How many protons are present in an atom of potassium-29?
2. Atoms & Elements
Isotopes
Struggling with General Chemistry?
Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
Which element has a mass number of 7 and contains 3 protons?
A
Boron
B
Helium
C
Beryllium
D
Lithium
Verified step by step guidance1
Identify the number of protons in each element option: Boron (5 protons), Helium (2 protons), Beryllium (4 protons), and Lithium (3 protons).
Recall that the mass number of an element is the sum of its protons and neutrons.
Given that the element has a mass number of 7 and contains 3 protons, calculate the number of neutrons by subtracting the number of protons from the mass number: 7 - 3 = 4 neutrons.
Verify which element has 3 protons and a mass number of 7 by checking the periodic table or known atomic numbers.
Conclude that Lithium, with 3 protons and 4 neutrons, matches the criteria of having a mass number of 7.
Related Videos
Related Practice
