Question
Which atom contains exactly $15$ neutrons?

Answer

mass number $=$ no. of protons $+$ no. of neutronsGiven that mass number of $P = 32$
Atomic number $($no. of electrons $=$ no. of protons$) = 17$
Number of neutrons $= 32 − 17 = 15$
Hence, $P$ satisfies the requirement.

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