Increasing order of electro negativity is

The correct option is Bi < P < S < Cl.

To understand the increasing order of electronegativity for the given elements (Bismuth ($\mathrm{Bi}$), Phosphorus ($P$), Sulfur ($S$), and Chlorine ($\mathrm{Cl}$)), we can analyze their positions in the periodic table and the general periodic trends of electronegativity.

1. General Periodic Trends:
- Across a Period (Left to Right): Electronegativity increases because the effective nuclear charge increases and the atomic radius decreases, which stronger attracts shared electrons.
- Down a Group (Top to Bottom): Electronegativity decreases because the atomic radius increases and the shielding effect increases, making the nucleus less effective at attracting shared electrons.

2. Group and Period Positions:
- Bismuth ($\mathrm{Bi}$) and Phosphorus ($P$) belong to Group 15 (Nitrogen family). Phosphorus is in Period 3, while Bismuth is in Period 6. Since electronegativity decreases down a group:
${\chi }_{\mathrm{Bi}}<{\chi }_P$
- Phosphorus ($P$), Sulfur ($S$), and Chlorine ($\mathrm{Cl}$) are all in Period 3, belonging to Groups 15, 16, and 17, respectively. Since electronegativity increases from left to right across a period:
${\chi }_P<{\chi }_S<{\chi }_{\mathrm{Cl}}$

3. Combining the Trends:
Combining these relations gives:
$\mathrm{Bi}<P<S<\mathrm{Cl}$
Therefore, the electronegativity increases in the order: Bismuth < Phosphorus < Sulfur < Chlorine.