If an element has an atomic number of 12 how many protons does each atom have?

What’s the scientific notation for the number 6,840,000,000

Kc = 0.040 for the system below at 450oc. if a reaction is initiated with 0.40 mole of cl2 and 0.40 mole of pcl3 in a 2.0 liter container, what is the equilibrium concentration of cl2 in the same system? pcl5(g) ⇄ pcl3(g) + cl2(g)

The identities of substances are the same before and after which type of change