Astrontium-90 atom that has lost 2 electrons has protons, neutrons, and electrons.

For an atom, the atomic number is equal to number of protons and number of electrons. Mass number is sum of number of protons and neutrons in nucleus of an atom. Atomic number is denoted by symbol Z and mass number is denoted by symbol A.

The atomic number of strontium is Z=38 and mass number is A=90.

Now,

Also,

Putting the value of in above equation,

Or,

Thus, number of neutrons are 52.

Now, after losing two electrons, number of protons and neutrons remains the same but number of electrons becomes 38-2=36

Therefore, a strontium-90 atom that has lost 2 electrons has 38 protons, 52 neutrons and 36 electrons.