Question

Which of the following correctly identifies an exception to the order of the periodic table?

A.) Hydrogen is the only Noble Gas found in Group 1
B.) Cobalt is located before Nickel even though it has a higher average atomic mass.
C.) Boron has 8 protons even though its atomic number is 5
D.) Bromine is the only noble gas not found in group 18

Answer 1

The exception in the order of the periodic table is;

B.) Cobalt is located before Nickel even though it has a higher average atomic mass

Step-by-step explanation:

The Russian chemist Dmitri Mendeleev who formulated the periodic law, observed that the arrangement of the atoms in an order of their increasing atomic mass resulted in a table that show a recurring pattern in the properties of the elements within each group

However, cobalt (atomic mass 58.93 amu) which was heavier than nickel (atomic mass 58.71) was placed before nickel due to the similarities of its chemical properties to the group in which it was placed

It was later observed that cobalt with 27 protons was rightly placed to come before nickel that has 28 protons in the periodic table classified by atomic numbers which is the proton number.