Consider the nuclear equation. 56124Ba→55124Cs+? Which completes the nuclear equation?

The mass number stays 124, while the atomic number decreases from 56 for barium to 55 for cesium. The missing particle must therefore have mass number 0 and atomic number +1, so it is a positron, written +1⁰e. Choice C, “+1⁰e,” completes the equation.

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