atoms and molecules

hello every one ...
                today in this article i will tell about
                                                                 ATOMS AND MOLECULES

• During a chemical reaction , the sum of the masses of the reactants and products remain uncharged . this is known as the law of conservation .
• Mass of 1 mole of a substance is called its molar mass .
•  In  a pure chemical compound , elements are always in a definite proportion by mass . 

  NOW THERE ARE SOME QUESTIONS FOR STUDENTS OF CLASS 9 . 

Q1 . WHAT IS THE CHEMICAL FORMULA OF MAGNESIUM CHLORIDE ?

Q2 . WHAT IS THE CHEMICAL FORMULA OF  COPPER NITRATE ?

Q3. WHAT IS THE MASS OF 3 MOLE OF NITROGEN ? 

Q4 CONVERT INTO MOLES  - 

1.  30 g OF OXYGEN GAS 
2. 40 g OF WATER 
3.  20 g OF CARBON DIOXIDE