CBSE Questions for Class 7 Chemistry Physical And Chemical Changes Quiz 5 - MCQExams.com

Rusting can be prevented by:
  • coating the object with paint
  • coating the object with grease
  • galvanizing
  • All of the above
What are the essential conditions for rusting to take place?
  • Presence of pure water
  • Presence of oxygen
  • Presence of water
  • Presence of oxygen alone is enough
Which one of the following is responsible for converting milk into curd?
  • Fungi
  • Bacteria
  • Virus
  • None of the above
What are the different conditions for a chemical reaction to take place?
  • Close contact
  • Solution form
  • Heat
  • Light
  • All of these
What type of protection is galvanising?
  • Physical protection
  • Sacrificial protection
  • Physical and sacrificial protection
  • None of the above.
While forming crystals, it is important to :
  • evaporate to dryness to get purest possible crystals.
  • attach gas syringes to collect fumes.
  • not evaporate water of crystallization.
  • use high flames.
Which of the following is true?
  • Rusting will take place in absence of water.
  • Rusting will take place in absence of air.
  • Rusting will not take place in presence of water and air.
  • None of the above.
One of most common solvent used for crystallization is:
  • Syrup
  • Normal saline
  • Water
  • Sulphuric acid
Insoluble impurities from solution during crystallization are removed by :
  • drying
  • filtration
  • heating
  • cooling
Large crystals of pure substances can be formed from their solutions during ____________.
  • crystallization
  • evaporation
  • expansion
  • contraction

Take some clean iron nails and place them in the three test tubes prepared as under:

Test tube A: Contains boiled water and a thin layer of oil.

Test tube B: Contains dry air.

Test tune C: Testube half-filled with water. 

All the test tubes are tightly closed after placing the nails. After some time what will you observe?
  • Nails placed test tube A rust.
  • Nails placed test tube B rust.
  • Nails placed test tube C rust.
  • None of these
Which of the following is/are true when milk changes into curd?
(i) Its state is changed from liquid to semi-solid.
(ii) It changes colour.
(iii) It changes taste.
(iv) The change cannot be reversed.
  • $$i, ii$$
  • $$ii, iii$$
  • $$i, iii, iv$$
  • $$i, iv$$
Changes in which only ____________ properties of a substance change are called physical changes.
  • chemical
  • physical
  • biological
  • environmental
State true or false.
Formation of manure from leaves is a physical change.
  • True
  • False
Iron pipes coated with zinc do not get rusted easily.
  • True
  • False
Condensation of steam is not a chemical change.
  • True
  • False
State whether true or false:

Cutting a log of wood into pieces is a chemical change.
  • True
  • False
State true or false.
Iron and rust are the same substances.
  • True
  • False
Chemical changes are:
  • those that are reversible
  • those in which new substances are formed
  • those that do not release heat
  • All of these
The process of obtaining salt by evaporation of seawater is known as :
  • crystallization
  • sedimentation
  • galvanization
  • amalgamation
Conversion of milk into curd is :
  • a physical property of milk
  • a chemical property of milk
  • a physical change
  • a chemical change
Dissolving sugar in water is an example of:
  • physical change
  • chemical change
  • neutralisation
  • None of these
Which conditions are necessary for rusting?
  • Oxygen
  • Sunlight, water and metal
  • Water, oxygen, a metal
  • Metal and oxygen
What is the difference between iron and aluminium with respect to corrosion?
  • Aluminium does not corrode
  • Corroded iron is soluble in water
  • Aluminium corrodes but iron does not corrode
  • Aluminium is less reactive than iron and so corrodes less
What effect does salt have on the corrosion of iron?
  • Absolutely none
  • Speeds up the reaction
  • Stops rust in it's tracks
  • Gives off a different type of rust
Which of the following represents correct statement(s)?
  • Salt can be obtained by the evaporation of sea water.
  • The salt obtained during crystallisation is pure and its crystals are large.
  • After crystallisation, the shape of the crystals can be seen clearly.
  • Large crystals of pure substances cannot be formed from their solutions.
State true or false.
Crystallisation is an example of chemical change.
  • True
  • False
When a magnesium ribbon burns in air, the ash formed is dissolved in water:
  • the solution of ash in water is basic in nature
  • the solution of ash in water is acidic in nature
  • the solution of ash in water is neutral in nature
  • none of these
Brown colour formation in an exposed apple after it's cut is:
  • physical change
  • chemical change
  • reversible change
  • no change
The freezing point of pure water is ____________.
  • 100 degree centigrade
  • 50 degree centigrade
  • 20 degree centigrade
  • zero degree centigrade
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