A calorie is not a metric unit but the joule is, 1 calorie is approximately 4.2 joule.
A gram of hydrogen does not exactly have 1 mole of particles. The historical definition for the mole was the count of atoms in 12 grams of the ¹²C carbon isotope, which is slightly different.
I like beeing pedantic. Please proceeed.
A calorie is not a metric unit but the joule is, 1 calorie is approximately 4.2 joule. A gram of hydrogen does not exactly have 1 mole of particles. The historical definition for the mole was the count of atoms in 12 grams of the ¹²C carbon isotope, which is slightly different.