The term "periodic" identify that occur in the table, like electronegativity or atomic radii.
a.) atomic mass
b.) families
c.) patterns

option C= patterns

Explanation:

The periodic table is helpful to identify the element readily. All the elements are arranged properly. The elements with same physical and chemical properties are placed in same group and period. Periodic table is also helpful to predict the properties of those elements which are not discovered yet. This table is also very helpful to balance the chemical equations. The horizontal rows are called periods while vertical column are called groups. There are seven periods and eighteen groups are in periodic table.

Trends in periodic table:

As we move left to right in a period the atomic radius is decreases with increase of atomic number. The ionization energy goes to increases from left to right in period because of greater hold of nuclear charge on valance electron, so that's way more energy is required to overcome this charge and to make the atom ionic.

From left to right in period electron affinity and electronegativity also increases.

As we move top to bottom in group ionization energy decreases with increase of atomic number  because of large atomic radius. The valance electron require less energy to move free. The electron affinity and electronegativity also decreases from top to bottom.

1. a)c-14 has two more protons

2. d)they have different numbers of protons, neutrons, and valence electrons; they are all gases at room temperature.

3. c) iron and nickel.