1. The reaction of H2 gas with oxygen gas to form water is an example of ?

exothermic reaction

all of these reactions

combination reaction

redox reaction

Answer: combination reaction

Explanation:


2. Which of the following is a physical change ?

Getting salt from sea water

Burning of wood

Formation of curd from milk

Ripening of fruits

Answer: Getting salt from sea water

Explanation:


3. Give the ratio in which hydrogen and oxygen are present in water by volume ?

1:8

1:2

1:1

2:1

Answer: 1:2

Explanation:


4. Which Of The Following Processes Involve Chemical Reactions ?

Liquefaction of air

Heating copper wire in the absence of air at high temperature

A storing of oxygen gas under pressure in a gas cylinder

Keeping petrol in china dish in an open

Answer: Heating copper wire in the absence of air at high temperature

Explanation:

During a chemical reaction the chemical composition of a substance changes. A chemical reaction produces a new substance with new properties. Energy is either released or absorbed during a chemical reaction. It is an irreversible reaction. You can easily understand by this equation: 2CU (copper wire) + O2 -> 2CuO (copper oxide)


5. The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and taste is called ?

Corrosion

Rancidity

Reduction

Antioxidation

Answer: Rancidity

Explanation:


6. A substance added to food containing fats and oils is called ?

Antioxidant

Oxidant

Rancid

Coolant

Answer: Antioxidant

Explanation:


7. The process of reduction involves ?

removal of hydrogen

removal of oxygen

addition of hydrogen

addition of oxygen

Answer: addition of hydrogen

Explanation:


8. The reaction in which two compounds exchange their ions to form two new compounds is ?

a double displacement reaction

a displacement reaction

an isomerization reaction

a decomposition reaction

Answer: a double displacement reaction

Explanation:


9. Which Of The Following Is Not A Physical Change ?

Dissolution of salt in water

Combustion of Liquefied Petroleum Gas (LPG)

Boiling of water to give water vapour

Melting of ice to give water

Answer: Combustion of Liquefied Petroleum Gas (LPG)

Explanation:

LPG on combustion produced carbon dioxide, water and heat is produced. This reaction is irreversible. Thus combustion of LPG is not physical change.


10. When green coloured ferrous sulphate crystals are heated, the colour of the crystal changes because ?

it loses water of crystallisation

it forms SO3

it is decomposed to ferric oxide

it forms SO2

Answer: it loses water of crystallisation

Explanation: