Answer
Cr-50 has 24 protons and 26 neutrons
Cr-52 has 24 protons and 28 neutrons
Cr-53 has 24 protons and 29 neutrons
Cr-54 has 24 protons and 30 neutrons
The atomic mass is 51.9961 amu
Work Step by Step
The atomic number for Chromium is 24. The number of neutrons is the difference between the atomic mass and the number of protons
Cr-50 has 24 protons and 26 neutrons
Cr-52 has 24 protons and 28 neutrons
Cr-53 has 24 protons and 29 neutrons
Cr-54 has 24 protons and 30 neutrons
$A_{Cr}$ = $\frac{4.345}{100}$ x 49.946 + $\frac{83.79}{100}$ x 51.9405 + $\frac{9.5}{100}$ x 52.9407 + $\frac{2.365}{100}$ x 53.9389 = 51.9961 amu