Invisible stage of M-phase is

Options

A. `G_(1)`-phase
B. S-phase
C. `G_(2)`-phase
D. `G_(0)`-phase

Answer

### Step-by-Step Solution:

1. **Understanding the M-phase**: The M-phase, or mitotic phase, is the part of the cell cycle where cell division occurs. It includes processes such as mitosis and cytokinesis.

2. **Identifying the Stages of the Cell Cycle**: The cell cycle consists of several phases, including G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). There is also a resting phase known as G0.

3. **Defining the Term "Invisible Stage"**: In the context of the question, the term "invisible stage" refers to a phase in the cell cycle where the chromosomes are not visible under a light microscope.

4. **Analyzing the Options**:
- **Option 1: G1 phase** - This phase is visible as the cell grows and prepares for DNA replication.
- **Option 2: S phase** - This is the phase where DNA is replicated. During this phase, the chromosomes are not yet condensed and are therefore not visible under a light microscope, making it the "invisible stage."
- **Option 3: G2 phase** - This phase occurs after DNA replication and is also visible as the cell prepares for mitosis.
- **Option 4: G0 phase** - This is a resting phase where the cell is not actively preparing to divide, but it is still visible.

5. **Conclusion**: Based on the analysis, the correct answer to the question "Invisible stage of M-phase is" is **Option 2: S phase**. This phase was historically referred to as "invisible" because the chromosomes are not visible under a light microscope.