The balanced chemical equation representing the neutralization reaction of hydrochloric acid (HCl) and sodium hydroxide (NaOH),

This reaction is exothermic that is it proceeds by the release of heat energy. This heat energy is lost to the surroundings. This is the reason for the warming up of the beaker where the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) takes place. The enthalpy of such reaction will be negative as the reaction is exothermic.
The answer is A: Between 50 and 5,000 amino acids
it would be species in this case
Electrons = protons
protons = atomic number
protons + neutrons = atomic mass
Therefore: a) protons + 7 = 15
protons= 15 -7
protons= 8
B) Remember proton = atomic number
so atomic number = 8
C)Now we know the atomic number so we can easily check on the periodic table what element has an atomic number of 8, which is Oxygen