A student adds a small quantity of caustic soda 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) a clear transparent colourless solution

(b) clear transparent pink solution

(c) a precipitate settling at the bottom of the test tube

(d) formation of bubble