An atom of the isotope Cs contains how many protons (p)?

• A. 47
• B. 133
• C. 55
• D. 78

Answer: (C)

Verified step by step guidance

1. Identify the element symbol given, which is Cs. This symbol corresponds to the element Cesium on the periodic table.
2. Recall that the number of protons in an atom is equal to the atomic number of the element. The atomic number is unique for each element and is found on the periodic table.
3. Look up the atomic number of Cesium (Cs) on the periodic table. This number tells you how many protons are in one atom of Cesium.
4. Understand that the isotope number (such as 133 in Cs-133) represents the sum of protons and neutrons, but does not affect the number of protons.
5. Conclude that the number of protons in an atom of Cesium is equal to its atomic number, which is 55.