___Al2(Cr2O7)3 + ___(NH4)3PO4 --> ___AlPO4 + ___(NH4)2Cr2O7

relative humidity is a measure of the amount of moisture in the air relative to the total amount of moisture the air can hold.

so d

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.