Resistance of 50W bulb is more than that of 100W bulb. Then which bulb will glow more brightly?

You have a relatively common question.  I have taught high
school science for 10 years and electricity is often a difficult topic for students to
understand because of all the different units, formulas,
etc.

Your question involves resistance and electrical
power, which are two different things.  When concerned with issues of resistance, Ohm's
Law is used to calculate its resistance.  Ohm's Law states that Voltage (measured in
volts) = Current (in amperes) x Resistance (measured in Ohms).  To solve for resistance,
the formula would be rearranged and resistance = voltage / current.  Watts are the unit
of electrical power.  Electrical power = current x voltage; therefore, the brightness of
the bulb doesn't have to do with amount of resistance.  It actually has to do with the
amount of current and voltage.

My suggestion to you is to
get a good set of notes on a level you understand (regardless of your grade level) and
get some wire, batteries and light bulbs and try several configurations to help you
understand.  The very small lights like those that go on Christmas trees are the best
for this small experiment.

I hope that this
helps.