Explanation:

When a 40-watt lamp is connected in series with a 100-watt lamp across a 220 V supply, the lamps share the voltage in proportion to their power ratings. According to Ohm's law, the current flowing through a circuit is directly proportional to the voltage and inversely proportional to the resistance.

1. Voltage distribution:
- The total voltage across the series combination of lamps is 220 V.
- Let's assume the voltage across the 40-watt lamp is V1 and the voltage across the 100-watt lamp is V2.
- Since the lamps are connected in series, the total voltage is divided between them.
- Therefore, V1 + V2 = 220 V.

2. Power distribution:
- The power consumed by a device is given by the formula P = VI, where P is the power, V is the voltage, and I is the current.
- Using this formula, the power consumed by the 40-watt lamp can be written as P1 = V1 x I1, and the power consumed by the 100-watt lamp can be written as P2 = V2 x I2.
- Since the lamps are connected in series, the current passing through both lamps is the same.
- Therefore, I1 = I2.

3. Relationship between power and voltage:
- The power consumed by a device is directly proportional to the voltage across it.
- Mathematically, P = V x I.
- As the voltage across the lamps is divided in proportion to their power ratings, the 100-watt lamp will have a higher voltage compared to the 40-watt lamp.
- Therefore, V2 > V1.

4. Brightness of the lamps:
- The brightness of a lamp is directly proportional to the power consumed by it.
- Since P = V x I, the lamp with a higher power rating will consume more power and, therefore, glow brighter.
- In this case, the 100-watt lamp has a higher power rating than the 40-watt lamp.
- Thus, the 100-watt lamp will glow brighter than the 40-watt lamp.

Conclusion:
Based on the above analysis, the correct answer is option 'b' - the 40-watt lamp will glow brighter.