One mole of a symmetrical alkene on ozonolysis gives two moles of
an aldehyde having a molecular mass of 30u. The alkene is:

Options

A. ethene
B. propene
C. `1-`butene
D. `2-`butene

Answer

To solve the problem, we need to determine which symmetrical alkene, when subjected to ozonolysis, yields two moles of an aldehyde with a molecular mass of 30u.

### Step-by-Step Solution:

1. **Understanding Ozonolysis**: Ozonolysis is a reaction where alkenes react with ozone (O3) to form ozonides, which can be further reduced to yield aldehydes or ketones. The products depend on the structure of the alkene.

2. **Identifying Symmetrical Alkenes**: The problem specifies a symmetrical alkene. The common symmetrical alkenes include ethene (C2H4) and 2-butene (C4H8). We will analyze these two options.

3. **Analyzing Ethene (C2H4)**:
- The structure of ethene is H2C=CH2.
- Upon ozonolysis, ethene forms an ozonide which, when reduced (using Zn/H2O), yields two moles of formaldehyde (HCHO).
- The molecular mass of formaldehyde (HCHO) is calculated as follows:
- H: 1u (2 H atoms) = 2u
- C: 12u (1 C atom) = 12u
- O: 16u (1 O atom) = 16u
- Total = 2u + 12u + 16u = 30u

4. **Analyzing 2-Butene (C4H8)**:
- The structure of 2-butene is CH3-CH=CH-CH3.
- Upon ozonolysis, 2-butene forms an ozonide which, when reduced, yields two moles of acetaldehyde (CH3CHO).
- The molecular mass of acetaldehyde (CH3CHO) is calculated as follows:
- H: 1u (4 H atoms) = 4u
- C: 12u (2 C atoms) = 24u
- O: 16u (1 O atom) = 16u
- Total = 4u + 24u + 16u = 44u

5. **Conclusion**: Since the molecular mass of the aldehyde produced from 2-butene is 44u, it does not match the requirement of 30u. Therefore, the only alkene that fits the criteria is ethene.

### Final Answer:
The symmetrical alkene is **Ethene (C2H4)**.