21.

Which one of the following is not a natural fibre?

• Silk
  
  

• Acrylic
  
  

• Cotton
  
  

• Jute

A man goes door to door posing as a goldsmith. He promises to bring back the glitter on dull gold ornaments. An unsuspecting woman gives a set of gold bangles to him which he dips in a particular solution. The bangles sparkle but their weight has considerably reduced. The solution used by the impostor probably is

• conc. HCl

• a mixture of conc. HCl and conc. HNO₃

• conc. HNO₃

• dil. HCl

A teacher plans to teach 'Components of Food' in Class-VI. Which of the following can be used as an essential question?

• Why does your mother serve you a meal with a variety of food items?

• Does your mother prepare a definite set of food items for lunch every day?

• Do you eat all the items served in your lunch every day?

• List the food items your mother serves you in lunch

When an iron nail is dipped in copper sulphate solution, the colour of copper sulphate solution fades and a brownish layer is deposited over the iron nail. This is an example of

• decomposition reaction

• double displacement reaction

• displacement and redox reactions

• combination reaction

Bleeding is stopped by the application of alum to a wound because

• alum coagulates the blood and forms a clot

• alum reduces the temperature near the wound

• alum is an antiseptic

• the wound is plugged by the alum chunk

Non-metallic oxides

• are basic in nature

• are amphoteric in nature

• turn red litmus paper blue

• are acidic in nature

A doctor prescribes a medicine to treat hyperacidity. The main ingredient of the medicine is

• MgCl₂

• CaCO₃

• Na₂CO₃

• Al(OH)₃

The inner surfaces of food cans are coated with tin and not with zinc because

• zinc is more reactive than tin

• zinc has a higher melting point than tin

• zinc is less reactive than tin

• zinc is costlier than tin

While diluting sulphuric acid, it is recommended that the acid should be added to water because

• acid may break the glass container

• dilution of acid is highly exothermic

• dilution of acid is highly endothermic

• acid has strong affinity for water

Given below are a few chemical processes
A. Rusting of iron
B. Burning of a candle
C. Respiration
D. Photosynthesis'

Which two of these represent slow combustion? 

• D and A

• A and C

• B and C

• B and D