Explanation:

To understand why perchloric acid does not give a solution of strength 1 N when dissolved in 1 liter of water, we need to look at the concept of normality and the dissociation behavior of acids.

Normality (N) is a measure of concentration and represents the number of gram equivalent weights of a solute per liter of solution. For acids, the gram equivalent weight is equal to its molecular weight divided by the number of acidic hydrogen atoms it can donate.

Dissociation of Acids:
Acids dissociate in water to release hydrogen ions (H+), which are responsible for their acidic properties. The extent of dissociation determines the concentration of H+ ions in the solution. Let's analyze the dissociation behavior of the given acids:

a) HCl (Hydrochloric acid):
HCl is a strong acid and dissociates completely in water to produce H+ and Cl- ions. Therefore, when 1 mole of HCl is dissolved in 1 liter of water, it will give a solution of strength 1 N. (1 mole of HCl = 1 mole of H+ ions)

b) Perchloric acid (HClO4):
Perchloric acid is also a strong acid and undergoes complete dissociation in water to produce H+ and ClO4- ions. However, the molecular weight of perchloric acid (HClO4) is higher than that of hydrochloric acid (HCl). As normality is defined by gram equivalent weight per liter of solution, the higher molecular weight of perchloric acid will result in a lower normality value for the same number of moles. Hence, when 1 mole of perchloric acid is dissolved in 1 liter of water, it will not give a solution of strength 1 N. (1 mole of HClO4 = 1 mole of H+ ions, but the gram equivalent weight is higher than HCl)

c) HNO3 (Nitric acid):
Nitric acid is also a strong acid and completely dissociates in water to produce H+ and NO3- ions. Similar to hydrochloric acid, when 1 mole of HNO3 is dissolved in 1 liter of water, it will give a solution of strength 1 N. (1 mole of HNO3 = 1 mole of H+ ions)

d) Phosphoric acid (H3PO4):
Phosphoric acid is a weak acid and does not dissociate completely in water. It undergoes stepwise dissociation to produce H+ and H2PO4-, HPO42-, and PO43- ions. Each step of dissociation results in the release of one H+ ion. Therefore, when 1 mole of phosphoric acid is dissolved in 1 liter of water, it will give a solution of strength less than 1 N as only a fraction of H3PO4 molecules will dissociate to produce H+ ions. (1 mole of H3PO4 < 1="" mole="" of="" h+="" />

Conclusion:
Among the given acids, only perchloric acid (HClO4) does not give a solution of strength 1 N when dissolved in 1 liter of water. This is because perchloric acid has a higher gram equivalent weight compared to hydrochloric acid, resulting in a lower normality value for the