CBSE
CLASS 8
SCIENCE LESSON 4 METALS AND NON METALS
Q.1. GALVANISATION IS
Q2.ANODISING IS
Q.3.WHICH OF THE FOLLOWING IS AN ALLOY OF IRON
Q.4.THE REDUCING ACTIVITY OF SODIUM IS REDUCED BY
Q.5.THE HARDEST KNOWN SUBSTANCE IS
Q.6.NON METALS WHICH FORM OXIDES ARE
Answers
Answer:
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Q.1. ANS
Galvanization is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanizing, in which the parts are submerged in a bath of molten hot zinc.
Q.2. ANS
Anodising is an electrolytic process for producing thick oxide coatings, usually on aluminium and its alloys. The oxide layer is typically 5 to 30µm in thickness and is used to give improved surface resistance to wear and corrosion, or as a decorative layer.
Q.3. ANS
Invar is an alloy of iron. In this the alloying element is nickel and this alloy has a very low coefficient of thermal expansion.
Q.4. ANS
Potassium ( K ) Helps in reducing the Reducing Activity of Sodium ( Na ).
Q.5. ANS
Currently, diamond is regarded to be the hardest known material in the world. But by considering large compressive pressures under indenters, scientists have calculated that a material called wurtzite boron nitride (w-BN) has a greater indentation strength than diamond.
Q.6. ANS
Non-Metals that form Oxides are
(a) Bromine ( Br )
(b) Carbon ( C )
(c) Chlorine ( Cl )
(d) Nitrogen ( N )
(e) Hydrogen ( H )