# Calculate the number of neutrons present in the nucleus of an element X which is represented $_{15}^{31}\textrm{X}$

Mass number (A) = No. of protons (Z) + No. of neutrons

But the mass number is given as 31 and the number of protons is 15.

No. of protons (Z) + No. of neutrons = 31

Number of neutrons = 31 – number of protons

Number of neutrons = 31 - 15 = 16

16 neutrons are present in the nucleus of the element X.

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