60 W, 100 W and 1000 W bulbs are connected in parallel to the mains. The bulb that will be brightest is (all of them have same specified voltage)

For a parallel connection, power consumption is 

$P= \frac{V^2}{R}\Rightarrow P\propto \frac{1}{R}$

For the given bulbs, R can be calculated by 

$R = \frac{V^2}{P_{rated}}\Rightarrow R\propto \frac{1}{P_{rated}}$

Therefore, the 1000W bulb will be the brightest.