CBQ KVS RO GUWAHATI SCIENCE 10 -DEMO

Which of the following is not a physical change?

• Dissolution of NaCl in water
• Melting of ice to give water
• Combustion of Compressed Natural Gas(CNG)
• Boiling of water to give water vapour

Which of these is a convex mirror?

• Shaving mirror
• Dentist’s mirror
• Headlight mirror of a bike
• Rear-view mirror of a car

The brown gas evolved on heating of Lead nitrate is;

• Oxygen
• Nitrogen dioxide
• Nitrogen
• Nitric oxide

Magnesium ribbon is rubbed before burning because it has a coating of:-

• basic magnesium carbonate
• basic magnesium oxide
• basic magnesium chloride
• basic magnesium sulphide

Solution of slaked lime is used for white washing walls. Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls. Shiny finish of the walls after whitewashing is due to which of the following chemical compound :

• CaO
• Ca(CO3)2
• Ca CO3
• Ca(OH)2

You must have observed that iron articles are shiny when new, but get coated with a reddish brown powder when left for some time. This process is commonly known as rusting of iron. Some other metals also get tarnished in this manner. Have you noticed the colour of the coating formed on copper and silver? When a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion. The black coating on silver and the green coating on copper are other examples of corrosion. Why does silver chloride turns grey in sunlight ?

• Due to decomposition reaction
• Due to combination reaction
• Due to corrosion
• Due to electrolysis

A reaction occurred when substance A with atomic no 12 ribbon is rubbed and is allowed to burn in air , it burns with a dazzling white flame and changes into a white powder. 1. Identify the element A and white powder

• a) Mg, MgS
• b) Cu, CuO
• c) Al, Al2O3
• Mg, MgO

A mirror magnify the image of an object by minus 1.5 times which of the following is true about the image produced by the mirror.

• Image is real, erect and larger than the object
• Image is real, inverted and larger than the object
• Image is virtual and larger than the object
• Image is virtual and smaller than the object

The reaction is repeated with magnesium powder in place of magnesium ribbon under the same conditions. What will happen?

• Rate of reaction increase
• Rate of reaction become steady
• rate of reaction decrease
• no effect on the rate of reaction.

A student was–performing an activity to prove the requirements for photosynthesis. During this activity, he kept two identical healthy potted plants A and B in dark for 72 hours. After 72 hours, he covered plant A and B by bell shaped jars separately. While covering the plants with separate bell jars, he kept KOH in the watch glass by the side of the plant in setup A and not in setup B. Both these setups were made air tight and were kept in light for 6 hours. Then, Iodine Test was performed with one leaf from each of the two plants A and B.3. Which of the following statements shows the correct results of Iodine Test performed on the leaf from plant A and B respectively?

• Blue - black colour would be obtained on the leaf of plant A
• Blue - black colour would be obtained on the leaf of plant B
• Red colour would be obtained on the leaf of plant A
• Red colour would be obtained on the leaf of plant B