Answer: 1.36 M
Explanation:
Molarity of a solution is defined as the number of moles of solute dissolved per liter of the solution.

where,
n = moles of solute
To calculate the moles, we use the equation:
moles of solute= 

The balanced reaction between barium hydroxide and perchloric acid:

To calculate the concentration of acid, we use the equation given by neutralization reaction:

where,
are the n-factor, molarity and volume of acid which is 
are the n-factor, molarity and volume of base which is 
We are given:

Putting values in above equation, we get:

Thus the concentration of the acid is 1.36 M
16-18= -2 so it has a negative charge. Just subtract the electrons from the protons if you get a positive number it will have a positive charge and vice versa.
A single replacement reaction could look like this:
2FeCl3 + 3Ba ➡️ 3BaCl2 + 2Fe
In this reaction, the barium is replacing the iron bound to the chlorine.