Answer:
c. mass
Step-by-step explanation:
Chemical elements placed in a tabular form according to their atomic number is known as periodic table.
The elements located next to one another in a periodic table have similar mass. In a period, the mass number of adjacent element varies by very few atomic mass. For example, Potassium and calcium are placed adjacent to each other. Potassium has atomic mass: 39.10 u and calcium has 40.08 u. Similarly, Vanadium has atomic mass 50.94 u and Chromium has atomic mas 52.00 u lie adjacent to each other.