What is the colour of nitrogen gas ?

Which of the following statements are true regarding oxygen?

I. It reacts with non-metals to form oxides, which are basic in nature.

II. Ozone is an allotrope of oxygen.

III. It is soluble in acidic pyrogallol.

IV. It is slightly heavier than air.

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Which of the following statements, in connection with the properties of water, is/are correct? 

I. Water has a higher specific heat in comparison with other liquids.

II. Water has no dipole moment.

III. Water has a low heat of vaporisation.

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Which one of the following statements, regarding the property of hard water, is/are correct? 

I. Temporary hardness of water is due to the presence of soluble magnesium and calcium hydrogen carbonate.

II. Temporary hardness of water can be removed by boiling.

III. Calgon's method is applied to remove the temporary hardness of water.

IV. Permanent hardness of water is removed by Clark's method.

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