The incorrect statements are

Options

A. The isotopies of chlorine with mass number 35 and 37 exist in ratio 3:1 if its average atomic mass is 35.5
B. The mass of one amu is approximately `1.6xx10^(-24)g`
C. The number of molecules in 1 ml of gas at STP is called Loschmidt number
D. none of these

Answer

To determine which statements are incorrect, we will analyze each statement one by one.

### Step 1: Analyze Statement A
**Statement A:** The isotopes of a chlorine atom with mass numbers 35 and 37 exist in a ratio of 3:1 if its average atomic mass is 35.5.

**Solution:**
- The average atomic mass of chlorine is calculated using the formula:
\[ \text{Average Atomic Mass} = p \cdot m_1 + (1 - p) \cdot m_2 \]
where \( p \) is the fraction of the isotope with mass \( m_1 \) (35) and \( m_2 \) (37).
- Given that the average atomic mass is 35.5, we can set up the equation:
\[ 35.5 = p \cdot 35 + (1 - p) \cdot 37 \]
- Rearranging gives:
\[ 35.5 = 35p + 37 - 37p \]
\[ 35.5 = -2p + 37 \]
\[ 2p = 37 - 35.5 = 1.5 \]
\[ p = 0.75 \]
- Thus, the ratio of isotopes is:
\[ \text{Chlorine-35} : \text{Chlorine-37} = 0.75 : 0.25 = 3 : 1 \]
- **Conclusion:** Statement A is correct.

### Step 2: Analyze Statement B
**Statement B:** The mass of one atomic mass unit (amu) is approximately \( 1.6 \times 10^{-24} \) grams.

**Solution:**
- The atomic mass unit (amu) is defined as \( \frac{1}{12} \) of the mass of one carbon-12 atom.
- The mass of one carbon-12 atom is approximately \( 1.99 \times 10^{-24} \) grams.
- Therefore, the mass of one amu is:
\[ \text{Mass of 1 amu} = \frac{1.99 \times 10^{-24}}{12} \approx 1.66 \times 10^{-24} \text{ grams} \]
- **Conclusion:** The statement is approximately correct, thus Statement B is correct.

### Step 3: Analyze Statement C
**Statement C:** The number of molecules in one mole of gas at STP is called Avogadro's number.

**Solution:**
- Avogadro's number is defined as \( 6.022 \times 10^{23} \) molecules per mole.
- At Standard Temperature and Pressure (STP), one mole of an ideal gas occupies 22.4 liters, which is consistent with Avogadro's number.
- **Conclusion:** Statement C is correct.

### Step 4: Analyze Statement D
**Statement D:** None of the above statements are incorrect.

**Solution:**
- Since we have established that Statements A, B, and C are all correct, Statement D, which claims that none of the statements are incorrect, is itself correct.
- **Conclusion:** Statement D is correct.

### Final Conclusion
All statements A, B, and C are correct, which means the answer to the question "The incorrect statements are" is that there are no incorrect statements. Thus, the correct option is D: None of these.

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