Which of the following statement is not true for `._(1)H^(1),._(1)H^(2),._(1)H^(3)` respectively -

Options

A. They are isotopes of each other
B. They have similar electronic configuration
C. They exist in the nature in the ratio `1:2:3`
D. Their atomic masses are in the ratio `1:2:3`

Answer

To solve the question regarding the statements about the isotopes of hydrogen, we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Identify the Isotopes**:
The isotopes mentioned are \( _{1}^{1}H \) (Protium), \( _{1}^{2}H \) (Deuterium), and \( _{1}^{3}H \) (Tritium). All three have the same atomic number (1) but different mass numbers (1, 2, and 3 respectively).

**Hint**: Recall that isotopes are atoms of the same element with different numbers of neutrons.

2. **Check if They are Isotopes**:
Since all three have the same number of protons (1) and different numbers of neutrons (0 for Protium, 1 for Deuterium, and 2 for Tritium), they are indeed isotopes of each other.

**Hint**: Isotopes share the same atomic number but differ in mass number.

3. **Electronic Configuration**:
All three isotopes have one electron, leading to the same electronic configuration of \( 1s^1 \).

**Hint**: The electronic configuration is determined by the number of electrons, which is equal to the number of protons in a neutral atom.

4. **Natural Abundance Ratio**:
The natural abundances of these isotopes are approximately:
- Protium: 99.98%
- Deuterium: 0.0026% to 0.0184%
- Tritium: Trace amounts

Therefore, they do not exist in the ratio of 1:2:3 in nature.

**Hint**: Check the natural abundances of isotopes to determine their occurrence ratio.

5. **Atomic Mass Ratio**:
The atomic masses of the isotopes are:
- Protium: 1
- Deuterium: 2
- Tritium: 3

The ratio of their atomic masses is indeed 1:2:3.

**Hint**: Atomic mass is a key characteristic of isotopes and can be compared directly.

### Conclusion:
The statement that is **not true** is: "They exist in nature in the ratio 1:2:3." Therefore, the correct answer is option 3.