A student adds 2 mL of acetic acid to a test tube containing 2 mL of distilled water. He then shakes the test tube well and leaves it to settle for some time. After about 5 minutes he observes that in the test tube there is:

"A convex lens can form a magnified erect as well as magnified inverted image of an object placed in front of it." Draw ray diagram to justify this statement stating the position of the object with respect to the lens in each case.

An object of height 4 cm is placed at a distance of 20 cm from a concave lens of focal length 10 cm. Use lens formula to determine the position of the image formed.

A student. is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect. Draw ray diagram for the:

(i) Defect of vision and also

(ii) For its correction.

A student prepared 20% sodium hydroxide solution in a beaker to study saponification reaction. Some observations related to this are given below:

(I) Sodium hydroxide solution turns red litmus blue

(II) Sodium hydroxide readily dissolves in water

(III) The beaker containing solution appears cold when touched from outside

(IV) The blue litmus paper turns red when dipped into the solution

The correct observations are:

Hard water is not available for an experiment. Some salts are given below:

(I) Sodium chloride

(II) Sodium sulphate

(Ill) Calcium chloride

(IV) Calcium sulphate

(V) Potassium chloride

(VI) Magnesium sulphate

Select from the following a group of these salts, each member of which may be dissolved in water to make it hard.