It is important to balance the chemical equations to satisfy the law of conservation of mass. Which of the following statements of the law is incorrect?

1. The total mass of the elements present in the reactants is equal to the total mass of the elements present in the products.
2. The number of atoms of each element remains the same, before and after a chemical reaction.
3. The chemical composition of the reactants is the same before and after the reaction.
4. Mass can neither be created nor can it be destroyed in a chemical reaction.

Consider the following statements in connection with the functions of the blood vessels marked A and B in the diagram of a human heart as shown.

(i) Blood vessel A — It carries carbon dioxide rich blood from the lungs.

(ii) Blood vessel B — It carries oxygen rich blood from the lungs.

(iii) Blood vessel B — Left atrium relaxes as it receives blood from this blood vessel.

(iv) Blood vessel A — Right atrium has thick muscular wall as it has to pump blood to this blood vessel.

The correct statements are

1. (i) and (ii) only
2. (ii) and (iii) only
3. (ii), (iii) and (iv)
4. (i), (ii) and (iii)

The correct statements with reference to single celled organisms are:

(i) Complex substances are not broken down into simpler substances.

(ii) Simple diffusion is sufficient to meet the requirement of exchange of gases.

(iii) Specialised tissues perform different functions in the organism.

(iv) Entire surface of organism is in contact wih the environment for taking in food.

1. (i) and (iii)
2. (ii) and (iii)
3. (ii) and (iv)
4. (i) and (iv)

Which one among the following is not removed as a waste product from the body of a plant?

1. Resins and Gums
2. Urea
3. Dry Leaves
4. Excess water