Which of the statement are true?

Options

A. Law of constant compositon is true for all types of compounds.
B. Molar volume of a gas at standard conditions is `22.4 L`.
C. vapour density of a gas is twice of its molecula mass.
D. Atomic masses of most elements are fractional.

Explanation

To determine which statements are true, let's analyze each statement step by step.

### Step 1: Analyze the First Statement
**Statement:** Law of constant composition is true for all types of compounds.

**Analysis:**
- The law of constant composition states that a given compound always contains the same proportion of elements by mass, regardless of the sample size or source.
- This law holds true for most compounds but does not apply to non-stoichiometric compounds (which have variable compositions) or compounds made up of isotopes of different elements.

**Conclusion:** This statement is **false**.

### Step 2: Analyze the Second Statement
**Statement:** The molar volume of a gas at standard conditions is 22.4 liters.

**Analysis:**
- At standard temperature and pressure (STP), defined as 0 degrees Celsius (273 Kelvin) and 1 atm pressure, the molar volume of an ideal gas is indeed 22.4 liters.

**Conclusion:** This statement is **true**.

### Step 3: Analyze the Third Statement
**Statement:** Vapor density of a gas describes its molecular formula.

**Analysis:**
- Vapor density (VD) is defined as the mass of a certain volume of gas compared to the mass of an equal volume of hydrogen at the same temperature and pressure.
- The relationship is given by the formula:
\[ \text{Vapor Density} = \frac{\text{Molecular Mass}}{2} \]
- Therefore, the statement that vapor density of a gas describes its molecular formula is incorrect.

**Conclusion:** This statement is **false**.

### Step 4: Analyze the Fourth Statement
**Statement:** Atomic mass of most elements are fractional.

**Analysis:**
- The atomic mass of an element is often a weighted average of the masses of its isotopes, which can result in fractional values.
- Since many elements exist as a mixture of isotopes, their atomic masses are not whole numbers.

**Conclusion:** This statement is **true**.

### Final Summary of Statements:
- **Statement 1:** False
- **Statement 2:** True
- **Statement 3:** False
- **Statement 4:** True

### Correct Options:
The correct statements are **Statement 2 and Statement 4**.

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