We know that in periodic table if we move from left to right then the size of the element decreases. So In nature the smallest element is fluorine.So When it make a diatomic F2 element then the repulsion between the electrons become maximum which results in the increasing of bond length. same thing happens with oxygen as oxygen has less electron than F so its bond length becomes less than F. And Chlorine has larger size than F so its bond length becomes large.

Increasing Order of Bond Lengths:
The bond length refers to the distance between the nuclei of two bonded atoms. It is influenced by various factors such as the size of the atoms involved, the number of shared electrons, and the strength of the bond. In general, as the size of the atoms increases or the bond strength decreases, the bond length increases. Let's analyze the given options to determine the increasing order of bond lengths.

Option A: F2, N2, Cl2, O2
- Fluorine (F) is the smallest atom among the given elements. It has a high electronegativity and forms a strong bond. As a result, F2 is expected to have the shortest bond length.
- Nitrogen (N) is larger than fluorine but still relatively small. It also forms a strong bond, so N2 is expected to have a slightly longer bond length than F2.
- Chlorine (Cl) is larger than nitrogen and has a lower electronegativity. Thus, Cl2 is expected to have a longer bond length than N2.
- Oxygen (O) is larger than chlorine and has a higher electronegativity. Therefore, O2 is expected to have the longest bond length among the given options.

Option B: Cl2, O2, N2, F2
- This option suggests that chlorine (Cl2) has the shortest bond length, which is contrary to our expectations. The trend of increasing bond length with increasing atomic size and decreasing bond strength is not followed here.

Option C: F2, Cl2, O2, N2
- This option suggests that fluorine (F2) has the shortest bond length, which is in line with our expectations. However, the order of the remaining elements is reversed compared to the expected trend.

Option D: N2, O2, F2, Cl2
- This option suggests that nitrogen (N2) has the shortest bond length, which is contrary to our expectations. The trend of increasing bond length with increasing atomic size and decreasing bond strength is not followed here.

Conclusion:
The correct answer is option D (N2, O2, F2, Cl2). The order of the elements in this option follows the expected trend of increasing bond length with increasing atomic size and decreasing bond strength. Therefore, N2 has the shortest bond length, followed by O2, F2, and Cl2.