When two substances X and Y are mixed together, a new substance Z is formed with the evolution of heat. Properties of Z are different from those of X and Y. Is Z an element, compound or a mixture?
If water samples are taken from sea, rivers, clouds, lakes or snow, they will be found to contain hydrogen and oxygen in the appropriate ratio of 1 : 8. This illustrates which law of chemical combination?
What is Avogadro's number?
The number 6·023×1023 is called Avogadro’s number (NA).