When all the bulbs are connected in parallel, 100W bulb is brighter. But for series connection, 40W is brighter.
Power is V² / R .
So for 40W, 220V bulb: R = 220² / 40 = 1210 ohms
for 80W bulb : R = 220² / 80 = 605 ohms
for 60 W bulb R =
for 100 W bulb R = 484
Let the four bulbs be connected in series with 220V supply. So when bulbs are connected in Series, the bulbs draw same current. ie., power = I² R being largest the 40 W bulb will glow brighter. As power dissipated in it is highest.