Question

The lightest metal among the following is:
A. Cs
B. Be
C. Na
D. Li

Answer 1

Lightness of any metal, depends on its atomic weight. Atomic weight of any substance or element is calculated by adding the total mass of all the elements present. So, find out the atomic weights of each element that is given in the option and you will figure out which one is the lightest one.

Complete step by step solution:
- Coming to the first option, Caesium belongs to the first group and sixth period in the periodic table. It has a symbol as Cs and its atomic number is $55$. Its atomic weight is $132.9u$.
- The second option has beryllium, which belongs to the second group and second period. It is denoted with symbol Be and has atomic number as $4$. Its atomic weight is $9.01u$.
- Sodium, which is represented by the symbol Na is located in group one and period three. Its atomic number is $11$. Atomic weight of sodium is $23u$.
- While in the last option, lithium belongs to the second period and first group of the periodic table. Its atomic number is $3$ and atomic weight is $6.941u$.
So, from all the above we can see that the atomic weight of lithium is the lowest one. Thus, the lightest metal is lithium.

Hence, the correct option is D.

Note: Possibly you may get confused with the lightest metal and non-metal. There is no difference between both. Sometimes in question it is asked for the lightest metal and sometimes non-metal. Remember, every metal element’s lightness depends on its atomic weight.