What part of the atom determines the identity of an atom?

Amixture of gaseous sulfur dioxide and oxygen are added to a reaction vessel and heated to 1000 k where they react to form so3(g). if the vessel contains 0.669 atm so2(g), 0.395 atm o2(g), and 0.0851 atm so3(g) after the system has reached equilibrium, what is the equilibrium constant kp for the reaction: 2 so2(g) o2(g) ⇌ 2 so3(g)

Explain which group an element with the electron configuration 1s2 2s2 2p6 3s2 3p6 3d1 4s2 belongs to.

Which statement is best described as a atom