In the reaction

2H₂O $\stackrel{}{\rightleftharpoons }$ H₃O⁺ + OH^- , water is 

• a weak base

• a weak acid

• Both a weak acid and a weak base

• Neither an acid nor a base

Which of the following is/are used as bleaching agent?

• SO₂

• H₂S

• C_l2

• All of these

Which of the following metal is protected by its oxide layer

• Au

• Ag

• Al

•  Fe

Which of the following sample has greatest mass?

• 16.0 grams of O₂

• 0.8 mole of O₂

• 6.02 x10²³ molecules of O₂

• 20.4 L of O₂ at STP

When we add aluminum foil to freshly prepared sodium hydroxide solution a gas is produced. Which of the following correctly states the property of this gas?

• Colourless and odourless gas which extinguishes a burning match stick

• Colourless and odourless gas which promotes burning of a candle

• Brown coloured pungent-smelling gas

• Colourless and odourless gas which produces a 'pop' sound when a burning match stick is brought near

Aqueous solution of which of the following oxides will change the colour of blue litmus to red?

• Copper oxide

• Iron oxide

• Magnesium oxide

• Sulphur dioxide

You have phenolphthalein solution in three test tubes A, B and C. On putting 2-3 drops of dilute hydrochloric acid in A, a solution of sodium hydroxide in B and distilled water in C, if you immediately observe the colour of the solution in each test tube, you will find that the solution in test tube.

• A is colourless, in B pink and in C colourless

• A is pink, in B pale green and in C colourless

• A is colourless, in B colourless and in C pink

• A is pale green, in B pink and in C pink

A student puts a drop of dilute solution of sodium hydroxide first on a blue litmus paper and then on a red litmus paper. He would observe that

• the blue litmus paper turns red and the red litmus paper turns blue

• there is no change in the blue litmus paper and the red litmus paper turns blue

• there is no change in the red litmus paper and the blue litmus paper turns red

• the blue litmus paper turns colourless and there is no change in the red litmus paper

49.

When a copper plate is exposed to moist air for long, it acquires a dull green coating. The green material is

• copper sulphate

• a mixture of copper hydroxide and copper sulphate

• a mixture of copper carbonate and copper sulphate

• a mixture of copper carbonate and copper hydroxide

Which of the following set contains same number of molecules?
A. 1 gram O₂ , 2 gram SO₂
B. 1 gram CO₂ 1 gram N₂O
C. 1 gram CO₂ 1 gramN₂
D. 1 gram O₂ 1 gram O₃

• A, B and C

• A and B

• C and D

• All of these