F BLOCK is the block on the period table that contains the actinide series of elements.
Actinide series of elements are two rows under the periodic table which include Lanthanide series and Actinide series. These are all radioactive elements and all of these are not not found in nature. All these are included in F block element.
Explanation:
A chemical reaction equation that contains same number of atoms on both reactant and product side is known as a balanced chemical reaction equation.
For example, 
Here, number of reactant molecules are as follows.
Na = 2
S = 2
Cd = 1
O = 4
Number of product molecules are as follows.
Na = 2
S = 2
Cd = 1
O = 4
As there are already equal number of atoms on both reactant and product side. Hence, the reaction equation is balanced.
Also, in this reaction both
and
are present as aqueous solution. And, CdS is the precipitate that is formed as it is the insoluble solid that forms.
is present in aqueous state.
Protons have the same mass as B. Neutrons. They have almost the same exact mass.