It is the inorganic chemical 'beryllium di-chromate'.
Potassium Nitrate: Beryllium & Chromium
No, BeCr2O7 is not an empirical formula. Empirical formulas show the simplest whole-number ratio of atoms in a compound, while BeCr2O7 is a molecular formula that specifies the actual number of atoms present.
beryllium, Be, and chlorite, ClO2 . Be has a 2+ charge, and ClO2 has a 1- charge. To make a formula for beryllium chlorite, the charges must be balanced at 0. Since Be is 2+, and ClO2 is 1-, there needs to be 2 ClO2 to equal 0. +2 + -2=0. The formula is Be(ClO2)2
C2N2H8 can be reduced to an empirical formula by dividing all the numbers by 2. So its empirical formula is CNH4. None of the others can be reduced so they are all empirical formulas.