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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.