Which bulb will glow brighter?

Solution: 60 Watt bulb will glow brighter then 100 Watt bulb.
Why ?
When two bulb are connected in series across a power supply, the voltage drop across each bulb depends upon its resistance value.
60 Watt power value is less than 100 Watt. Which means 60 watt bulb must have higher resistance value to resist the current flow.
Let us consider,
Resistance of 60 watt bulb = R1
Resistance of 100 watt bulb = R2
Therefore,     R1  >  R2

We know that,
Voltage drop, V = IR
As R1 is greater than R2, therefore voltage drop across 60 watt bulb is more than 100 watt bulb. Hence 60W bulb will consume more power and glow brighter.
In Short, the voltage drop across 60W bulb is more than 100W because 60W bulb has higher resistance. Hence 60W bulb will glow brighter.