1.virtual image cannot be formed on screen but real image can be formed on screen. virtual image is always errect whereas real image is always inverted.
2. according to the law of conversation of mass when a chemical reaction occurs the mass of products and reactants must be equal.the amount of atoms in each element doesn't change in the chemical reaction.
e. Methanoic acid HCOOH. we can use baking soda to get rid from it .