Given below are events that lead to pregnancy and development of embryo
(i) Fertilization of egg
(ii) Maturation of egg
(iii) Release of egg
(iv) Embedding of embryo in thickened uterine wall.
Which of the following options gives the correct order of sequence in which they occur?

Options

A. i, ii, iii, iv,
B. ii, i, iii, iv
C. i, iv, ii, iii
D. ii, iii, i, iv.

Explanation

To determine the correct order of events that lead to pregnancy and the development of an embryo, we need to analyze the events provided:

1. **Maturation of egg (ii)**: This is the first step where the egg matures and becomes ready for fertilization.
2. **Release of egg (iii)**: After maturation, the egg is released from the ovary in a process called ovulation.
3. **Fertilization of egg (i)**: Once the egg is released, it travels to the fallopian tube where it can meet sperm for fertilization. This is the fusion of the sperm and egg, resulting in a zygote.
4. **Embedding of embryo in thickened uterine wall (iv)**: After fertilization, the zygote undergoes cell division to form an embryo, which then embeds itself into the thickened uterine wall in a process called implantation.

Now, putting these events in order:
- **(ii) Maturation of egg**
- **(iii) Release of egg**
- **(i) Fertilization of egg**
- **(iv) Embedding of embryo in thickened uterine wall**

Thus, the correct sequence of events is: **(ii) → (iii) → (i) → (iv)**.

The option that corresponds to this sequence is **2nd, 3rd, 1st, 4th**.

### Step-by-step Solution:
1. Identify the first event: **Maturation of egg (ii)**.
2. Identify the second event: **Release of egg (iii)**.
3. Identify the third event: **Fertilization of egg (i)**.
4. Identify the final event: **Embedding of embryo in thickened uterine wall (iv)**.
5. Arrange these events in the correct order: **(ii) → (iii) → (i) → (iv)**.
6. Choose the correct option that matches this sequence: **2nd, 3rd, 1st, 4th**.