Heavy water is the oxide of heavy hydrogen (deuterium) and is also called deuterium oxide. It is represented as `D_(2)O`. Heavy water is chemically similar to ordinary water heavy water is used for the neutron moderatory, as a trracer compound and for the preparation of deuterium. Reaction of heavy water with alkali metals liberates heavy hydrogen. heavy water can also be used for exchanging labile hydrogen with deuterium completely or partially. heavy water reacts slower than ordinary water but forms stronger bonds with other elements as compared to hydrogen.
Q. Which property of heavy water is lesser in magnitude as that compared with normal water?

Options

A. Molecular mass
B. Density
C. Boiling point
D. Ionisation constant

Answer

To solve the question regarding the properties of heavy water (D₂O) compared to normal water (H₂O), we will analyze the given options step by step.

### Step 1: Understand the Composition of Heavy Water
Heavy water is represented as D₂O, where D stands for deuterium, an isotope of hydrogen. The molecular formula of normal water is H₂O. The key difference is that in heavy water, the hydrogen atoms are replaced by deuterium atoms.

**Hint:** Remember that isotopes have different masses, which will affect the properties of the compounds they form.

### Step 2: Analyze Molecular Mass
The molecular mass of heavy water (D₂O) is greater than that of normal water (H₂O) because deuterium has a higher atomic mass (approximately 2) compared to normal hydrogen (approximately 1). Therefore, the molecular mass of D₂O is higher.

**Hint:** Compare the atomic masses of hydrogen and deuterium to understand how they affect the molecular mass of the compounds.

### Step 3: Analyze Density
Density is defined as mass per unit volume. Since heavy water has a higher molecular mass than normal water, it also has a higher density. Therefore, the density of D₂O is greater than that of H₂O.

**Hint:** Recall that if mass increases while volume remains constant, density will also increase.

### Step 4: Analyze Boiling Point
The boiling point of heavy water (D₂O) is higher than that of normal water (H₂O). The boiling point of normal water is 100°C, while that of heavy water is approximately 101.4°C. Thus, the boiling point of D₂O is greater than that of H₂O.

**Hint:** Look at the intermolecular forces and how they are affected by the mass of the molecules.

### Step 5: Analyze Ionization Constant
The ionization constant refers to the extent to which a substance can dissociate into ions. Heavy water (D₂O) has a lower ionization constant compared to normal water (H₂O). This is due to the isotopic effect, where the stronger bond formed between oxygen and deuterium results in less tendency for ionization.

**Hint:** Consider how the bond strength and molecular mass influence the ionization process.

### Conclusion
After analyzing all the options, we find that the property of heavy water that is lesser in magnitude compared to normal water is the **ionization constant**. Therefore, the correct answer is:

**Answer:** The ionization constant of heavy water (D₂O) is lesser in magnitude compared to that of normal water (H₂O).