In an experiment to study the properties of ethanoic acid, a student takes about 3 ml of ethanoic acid in a dry test tube. He adds are equal amount of distilled water to it and shakes the test tube well. After sometime he is likely to observe that

(a) List the parts of the human eye into it. Explain how they perform this function.

(b) Write the function of retina in human eye.

(c) Do you know that the corneal-impairment can be cured by replacing the defective cornea with the cornea of the donated eyes? How and why should we organize groups to motivate the community members to donate their eyes after death?

(a) Why do we classify elements?

(b) What were the two criteria used by Mendeleev in creating his Periodic Table?

(c) Why did Mendeleev leave some gaps in his Periodic Table?

(d) In Mendeleev's Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?

(e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.

A student takes about 2 mL ethanoic acid in a dry test tube and adds a pinch of sodium hydrogen carbonate to it. He reports the following observations:

I. Immediately a colourless and colourless gas evolves with a brisk effervescence.

II. The gas turns lime water milky when passed through it.

III. The gas bums with an explosion when a burning splinter is brought near it.

IV. The gas extinguishes the burning splinter that is brought near it.

The correct observations are

In a locality, hard water, required for an experiment, is not available. However, the following salts are available in the school laboratory:

1. Sodium sulphate 2. Calcium sulphate

3. Magnesium chloride 4. Sodium chloride

5. Calcium chloride 6. Potassium sulphate

Which of the above salts may be dissolved in water to obtain hard water for the experiment?