If an atom has 56 protons and 58 neutrons, how many electrons
would this atom have?

This atom would have 56 electrons.

Atomic Structure:

So, it is given that;

Number of protons=56

Number of neutrons=58

Thus, number of electrons=56 (since, the number of protons and number of electrons are same)

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Because the protons = the electrons so the atom will have 56 electrons.

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colorless gas, exhibiting a blue glow when placed in an electric field

b) solid

its a type of rock