No...neither of u are correct

The reason is plain......outward centrifugal force is balanced by inward centripetal force (Force of attraction by nucleus).......The 2 forces being opposite and equal cancel each other.

RATE!!!

http://www.cartage.org.lb/en/themes/Sciences/Chemistry/Inorganicchemistry/Informationbonding/Electrontunneling/electrontunneling.htm

What Hamba points out is a nice explanation but is untenable. The reason is due to Heisenberg Uncertainty Principle. I am a new member and am really surprised by the way people ask for rates :l

@ podolski

and I'm eally surprised the way idiots put forward their views!!!

Where comes heisenberg's principle in my answer???

podoloski has forgotten the basics of uncertainty principle........let him first decide whether uncertainty in vel. is 100% or not!!! 

 Well,  my first reply was a quick reply and I had hoped you people would see the link I had provided. But that does not seem the case, I shall prove why each answer put forth till now is not completely right and why the actual answer lies in the realm of quantum mechanics.

akshay's and angelboy's answer is based upon the Bohr atom of the model which has been outdated and has been replaced by the quantum mechanical model of the atom, and moreover Bohr's atomic model is wrong because it does not explain for the fact that an electron, unlike a planet or a satellite, is electrically charged, and it has been known since the mid-19th century that an electric charge that undergoes acceleration (changes velocity and direction) will emit electromagnetic radiation, losing energy in the process

 

@Hamba

The proposal, first made in 1913, that the centrifugal force of the revolving electron just exactly balances the attractive force of the nuceus (in analogy with the centrifugal force of the moon in its orbit exactly counteracting the pull of the Earth's gravity) is a nice picture, but is simply untenable: an electron, unlike a planet or a satellite, is electrically charged, and it has been known since the mid-19th century that an electric charge that undergoes acceleration (changes velocity and direction) will emit electromagnetic radiation, losing energy in the process.

Now, back to why I say the answer to the question lies in a proper understanding of Heisenberg's principle. To put it simply I quote from Feynman's  Lectures of Physics (Volume 1 pg 19-20) 

"What keeps the electrons from simply falling in?This principle: If they were in the nucleus, we would know their position precisely, and the uncertainty principle would require that they then have a large(but uncertain) momentum, i.e. a very large kinetic energy. With this kinetic energy they would break away from the nucleus..."

Also, the Heisenberg Indeterminancy ("uncertainty") principle requires the total energy of the electron energy to increase as the volume of space it occupies diminishes. As the electron gets closer to the nucleus, the nuclear charge confines the electron to such a tiny volume of space that its energy rises, allowing it to "float" slightly away from the nucleus without ever falling into it.

References: please look at them for a clear understanding:

http://www.cartage.org.lb/en/themes/Sciences/Chemistry/Inorganicchemistry/Informationbonding/Electrontunneling/electrontunneling.htm

Feynman Lectures on Physics: Volume 1 pg 19-20

PS: @Hamba; there is a civilised way in which one puts across his/her opinion. I would not mind if you contradict my answer or even rubbish it. But referring to people as "idiots" is unbecoming.

What do you mean "the question is of Bohr's model?" In the actual world, electrons fall into the nucleus or what?? Bohr's model does not explain the actual behaviour of electrons. So we have to explain all of it in terms of the quantum mechanical model. Unless its specified explicitly that you could use the Bohr's model.  I advice people to go through the full post.

 In whatever model you speak of there are electrons!! ... Let us not forget the basics. There are electrons present and its the aim of all these models to explain their behaviour. Electrons are not electron clouds in quatum mechanical theory. An electron exists but its probablity of location is maximum in a particular region, which is an electron cloud. As to this question of electron falling inside the nucleus, I am not providing any further clarifications. As for me, the fact that Feynman and the whole scientific community endorses my view settles it. Just refer the links and you shall get a better idea.

I really do not understand what u people are out with.....firstly someone pointed out abt the existance of electron clouds....and that's correct.....Podolski hs  forgotten the basics himself ( and like a bloke, he asks us to remember the basics), anyway.....so when the question is confined to Bohr's model....WHERE ON EARTH DO U ALL FIND UNCERTAINTY PRINCIPLE???

And as of teachers, they have forgotten that in deducing radii, energy of electrons, we equated mv²/r=Ze²/r².

WHAT EXPLANATION U GIVE FOR THAT DUDES???