Avogadro’s number is derived from the number of carbon-12 atoms in 12.00 grams. In a chemical reaction, 3.0 moles of hydrogen react with 4.0 moles of oxygen to produce water. How many reacting molecules are present when the reaction starts? A. 1.8 x 1024 molecules B. 6.0 x 1023 molecules C. 4.2 x 1024 molecules D. 2.4 x 1024 molecules