The events in sexual reproduction are
(i) pre-fertilisation
(ii)fertilisation
(iii) post-fertilisation
The sequential order of their occurrence is

Options

A. (ii)-(i)-(i)
B. (iii)-(ii)-(i)
C. (i)-(ii)-(iii)
D. (i)-(iii)-(iv)

Answer

To determine the sequential order of events in sexual reproduction, we need to analyze the three main stages: pre-fertilisation, fertilisation, and post-fertilisation. Here’s a step-by-step breakdown of these events:

### Step-by-Step Solution:

1. **Pre-fertilisation**:
- This is the initial stage where the body undergoes development and maturation.
- During this phase, gametes (sperm and egg) are produced through a process called gametogenesis.
- This stage involves growth and preparation for the next step, which is fertilisation.

2. **Fertilisation**:
- This is the second stage where the actual fusion of the male gamete (sperm) and the female gamete (egg) occurs.
- The result of this fusion is the formation of a zygote, which is the first cell of a new organism.
- Fertilisation is a crucial event as it leads to the combination of genetic material from both parents.

3. **Post-fertilisation**:
- In this final stage, the zygote undergoes a series of developmental processes.
- The zygote divides and develops into an embryo, which eventually will develop into a fully formed organism.
- This stage encompasses all the changes that occur after fertilisation until the organism is ready for birth or hatching.

### Conclusion:
The correct sequential order of the events in sexual reproduction is:
1. Pre-fertilisation
2. Fertilisation
3. Post-fertilisation

### Final Answer:
The sequential order of their occurrence is: **(i) Pre-fertilisation, (ii) Fertilisation, (iii) Post-fertilisation.**

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