As I have read , charge is electrons , protons or neutrons.
Electrons and protons are both particles that have a charge, and neutrons are uncharged.
Now , according to definition of current , current is the rate of flow of charge
Yes
I.e flow of electrons.
A flow of electrons will give you a flow of charge, or a current. A flow or movement of other charged entities (protons, ions, charged objects like the sectors of a Wimshurst machine) will also give you a current
Then , I=Q/t .
When measured in consistent units, yes. The I is in amperes, Q in Coulombs, t in seconds.
Unit of Q is coulomb & Q is charge.
A Coulomb is one unit of charge. There are other units of charge, like the electron charge, which is the charge on one electron, or the Faraday, which is the charge on a mole (about 6x10^23) of electrons. One Coulomb is the charge on about 6*10^18 electrons.
Right , so Coulomb is actually like the No of electrons flowing through the conductor.
No, you're getting your units mixed up here. The number of electrons flowing through a conductor is a number, a pure number, a counting number, without units. A Coulomb has units of charge.
Also , \$Q=n∗e\$
True if all quantities are in consistent units. For instance, if Q is in units of electron charge, n is a number, and e is one electron charge. Or if both Q and the electronic charge are measured in Coulombs.
But there is another point in my book that charge on an electron = −1.6∗10−19
I hope it doesn't say just that. It should say
charge on an electron = −1.6∗10−19 Coulombs
Now, this is confusing. Charge is electron , what does charge on an electron mean ? If charge is a like a numerical value , change on an electron means like there is some kind of energy the electron has. Is it that charge has two definitions?
An electron has charge, just like an electron has mass. They are both properties of an electron. A large number of electrons will have this much mass, or that much charge.
Charge is not like a numerical value. But the amount of charge can be measured as a number times a unit of charge.
Energy is a whole different ball-game, best to stay away from it in this level of discussion. Both charge and rest mass are intrinsic properties of an electron, it has them whatever the circumstances. When an electron is described as having energy, that's in some context of external fields or inertial frame, and is not an intrinsic property of the electron.
Also , if charge is a number. What does it mean by negative symbol for charge ?
It's just indicating that it's the opposite polarity to 'conventional positive charge', ie opposite to the charge on a proton.
Way back at the time of the Greeks, it was known that there were two polarities of charge, from friction charging of glass and amber. When modern experiments started, with Benjamin Franklin amongst many others, a convention was decided upon, for which to call positive and negative. When much later experiments revealed the structure of the atom, it was found that the convention labelled the proton charge as positive, and the electron as negative.
Some students think, or even insist, that this convention is wrong, as the first time they meet the concept of an electron, it's drifting along metal wires as an electric current. This insistence is just 'metallic conductor Chauvinism'. If you're in a profession where you really need to think about charge carriers, like semiconductors, plasma physics or electrolysis, then you might be dealing with holes or ions as well, and you need to treat all the charge carriers with their correct signs, and there's no practical preference for one or the other.
A convention is just that, a convention. If you stick to 'conventional' current, conventional charge, then it all works out.