Question

In the modern periodic table which one is the most correct about a period?

• A. The first element is an alkali metal and the last element is a halogen.
• B. The first element is a noble gas and the last one is an alkali metal.
• C. The first element is an alkali metal and the last element is a noble gas.
• D. The first element is an alkali metal except period 1 and the last element has 8 valence electrons.

Answer 1

The correct option is C

The first element is an alkali metal and the last element is a noble gas.

The elements in periodic table are placed in periods and groups. Periods are horizontal rows that has increasing atomic numbers. Groups are vertical columns. There are 7 periods and 18 groups in periodic table.

The explanation for the correct option:

Periods have different atomic number and different valence electrons count.

Since the first element of period have 1 valence electrons, they are named as alkali metals.

The last element of the period have fully filled valence shell and those elements are noble gases.

The explanation for the incorrect option:

The first element is alkali metal and last element is noble gas in a period.

The halogens belong to group 17 and that are not last elements of a period.

The last element in a period have completely filled electrons. Helium has only two electrons in valence shell.

Final answer:

Hence, option (C) is the correct option.