Answer: 19 protons are present in the given isotope.
Explanation: We are given a radioactive isotope [tex]^{40}_{19}K[/tex] and we need to find the number of protons in this isotope.
General representation of isotopes are given as:
[tex]^A_Z\textrm{X}[/tex]
Where, Z = Atomic number = Number of protons = Number of electrons
A = Atomic Mass = Number of protons + Number of neutrons
X = Element
In the given element K, Atomic number is 19 and mass number is 40.
As Z = 19,
Number of protons in given isotope = 19.
