Question

How many protons electrons and neutrons respectively does 29 CS have

Answer 1

$55 \; \text{e}^{-}$, $55 \; \text{p}^{+}$, and $74 \; \text{n}^{0}$- in case cesium-129 is what you were referring to.

Cesium has atomic number $55$ as seen on a modern periodic table. A cesium atom nucleus would thus contain an equal number of protons; in addition to that, a neutral atom of cesium would contain the same number of electrons in its electron cloud.

For a particular isotope,

$\text{Mass number} = \text{Number of protons per nuclei} + \text{Number of Neutrons per nuclei}$.

This isotope of cesium has a mass number of $129$ and contains $55$ protons in each atomic nucleus. One cesium nuclei would therefore contain $129 - 55 = 74$ neutrons.