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Right CHOICE is (d) PVC plastics are inflammable

The EXPLANATION: Plastics are ORGANIC in nature. They are not DUCTILE but have good electric insulation properties. Plastics made of PVC are non-inflammable.

The CORRECT choice is (a) 960 kg/m^3

To explain I would say: Fibreboards are rigid boards. They are also KNOWN as reconstructed wood. The maximum limit of WEIGHT of fibreboards is 960 kg/m^3. The weight depends on the pressure applied during their MANUFACTURING.

The correct choice is (a) Hard steel can be readily FORGED and welded

Best EXPLANATION: Hard steel has the following properties. Hard steel cannot be readily forged and welded. It RUSTS easily and can be magnetised permanently. The SPECIFIC gravity of hard steel is 7.90.

Correct choice is (a) Bow

To explain: Bow is a defect that occurs in the seasoning PROCESS of wood and is indicated by the curvature which FORMS in the direction of the length of timber. Blue stain, sap stain and brown rot are the DEFECTS caused in timber by FUNGI.

The correct choice is (d) Galena

Easiest explanation: The principle ores of copper are copper glance, malachite, azurite, CUPRITE and copper PYRITES. Copper is widely used for making electric CABLES, lighting conductors, household UTENSILS, etc. Galena is an IMPORTANT ore of lead.

The correct OPTION is (B) False

To explain: Copper mainly has two types of alloys – brass and BRONZE. Brass contains copper and zinc while bronze contains copper and tin. LOW brass contains 80% copper and 20% zinc.

Correct choice is (c) Impreg timber

For EXPLANATION I would say: Impreg timber is available under trade names such as FORMICA, SUNMICA, Sungloss, etc. It is the timber that is partly or fully covered with resin. Impreg timber is strong and durable.

Right CHOICE is (b) False

Easiest EXPLANATION: Chir and DEODAR are examples of softwoods while oak and SAL are examples of hardwoods. The terms hardwoods and softwoods have commercial importance only.

Correct answer is (b) DRAWING

The EXPLANATION is: The various operations involved in MECHANICAL treatment of STEEL are FORGING, drawing, pressing and rolling. Drawing is used to make wires and rods while forging is used to make bolts and cramps.

Correct ANSWER is (C) 1500 kg/m^3

Explanation: Mortars are classified into heavy mortars and lightweight mortars depending on the bulk density of MORTAR in its dry state. Heavy mortars have a bulk density equal to greater than 1500 kg/m^3 while lightweight mortars have a bulk density less than 1500 kg/m^3.

The CORRECT answer is (d) Ordinary plain round bars posses BETTER STRUCTURAL properties than these bars

For explanation I would say: Ribbed-torsteel bars are produced from ribbed-torsteel that is DEFORMED high STRENGTH steel. They possess excellent bonding properties and can be easily identified. They possess better structural properties than ordinary plain round bars and they serve as efficient concrete reinforcement.

Right ANSWER is (b) 0.35-0.45

To EXPLAIN I would say: The percentage of the copper content in copper STEEL VARIES from 0.15-0.25. Copper steel is a common variety of steel alloys that can RESIST atmospheric resistance better than ordinary carbon steel.

Right choice is (c) 10%, 85%

The explanation is: The percentage composition of copper in WHITE brass and red brass is RESPECTIVELY 10% and 85% respectively. Red brass contains 15% zinc with 85% copper while white brass contains 90% zinc and 10% copper.

The correct answer is (a) CASSITERITE

Easy explanation: The PRINCIPLE ores of magnesium are MAGNESITE, kieserite, DOLOMITE and carnallite. It does OCCUR in the free state in nature. Cassiterite is an oxide of tin.

The CORRECT option is (c) 3% iron, 37% ZINC and 60% copper

Easy explanation: The composition of delta metal is 3% iron, 37% zinc and 60% copper. Delta metal has high resistant to corrosion and can be used to RESIST corrosion in place of MILD steel.

Correct option is (a) True

For explanation: Polymerization is the process of CONVERTING monomers into POLYMERS. In addition, polymerization, the molecular weight of the resulting POLYMER is the same as the sum of the molecular WEIGHTS of the REACTING molecules.

The correct option is (a) True

Easiest explanation: On the BASIS of the size of grains, the sand is classified into three CATEGORIES – coarse, FINE and gravelly sand. Fine sand is GENERALLY USED for plastering. Coarse sand is used for masonry work and gravelly sand is mainly used for concrete work.

Right option is (c) Manganese

For EXPLANATION I would say: MOLYBDENUM STEEL CONSISTS of molybdenum and manganese. It contains molybdenum to the EXTENT of about 0.2-0.3 % and that of manganese is 0.7-1%.

The correct answer is (b) Monel METAL

Explanation: There are TWO main IMPORTANT alloys of nickel. These are Monel metal and nickel silver. Monel metal consists of COPPER and small percentages of other elements.

Right OPTION is (a) Aluminium is a POOR conductor of heat and ELECTRICITY

The explanation is: Aluminium is light in WEIGHT and readily dissolves in HCl. Aluminium is HIGHLY resistant to corrosion and is a good conductor of heat and electricity.

Correct choice is (c) CELLULOSE

To elaborate: Just like plastics, resins are ALSO classified into THERMOPLASTIC resins and thermosetting resins depending on their BEHAVIOUR with respect to HEATING. Cellulose is an example of thermoplastic resin. Phenol formaldehyde, casein and urea-formaldehyde are examples of thermosetting resins.

Correct answer is (a) It is POSSIBLE to change their shape on heating

To explain: Thermosetting PLASTICS BECOME rigid on heating and it is possible to change their shape. They are DURABLE and strong and are available in a variety of colours.

Right answer is (a) Speculum metal

Easy explanation: Delta metal and Muntz metal are the common varieties of brass which CONTAIN ZINC. GUNMETAL is a variety of bronze but FORMS an exception to their general rule and contains 2-4 % of zinc. Speculum metal does not contain zinc.

The correct choice is (d) Gold

For explanation: Dow metal is an important ALLOY of magnesium. It CONSISTS of 4-12 % aluminium, 0.1-0.4 % of MANGANESE and the rest is magnesium.

The correct answer is (d) It must contain salts that can attract MOISTURE from the atmosphere

For explanation I WOULD say: Good SAND should not contain salts that can attract moisture from the atmosphere and should be chemically inert. It should be CLEAN and should not contain any organic matter.

Correct option is (b) False

Explanation: The structure of BLISTER steel is not homogeneous. It is full of CAVITIES and cannot be USED for making EDGE tools.

The correct option is (d) Cast steel

For EXPLANATION: Steel produced by the crucible steel process is KNOWN as cast steel. A small QUANTITY of high CARBON steel is produced in this process. Cast steel is hard and is used for making surgical instruments.

Right choice is (c) Expansion and shrinkage are very high

To elaborate: Plywoods are light in weight. They are ELASTIC and are available in large SIZES. Expansion and shrinkage are RELATIVELY very LOW as plies are placed at an angle of 90° to each other.

Right OPTION is (c) It cannot be magnetised permanently

For EXPLANATION I would say: Mild steel has the following properties. Mild steel can be easily forged and welded and is ductile and MALLEABLE. It can be used for all TYPES of structural work and it can be magnetised permanently.

Right answer is (b) False

To explain I would say: Bronze is an alloy of copper and TIN but MANGANESE bronze consists of copper and zinc. The percentage of copper is generally from 56-60 and the REST is zinc. Other elements like manganese, LEAD, aluminium and iron are ALSO added.

Right answer is (B) 82%, 18%

The BEST explanation: Bell metal is a variety of BRONZE which is used for making bells. The PERCENTAGE of copper and tin in bell metal is 82% and 18% respectively.

Right choice is (a) Silver

Easiest EXPLANATION: Electron METAL is an alloy of MAGNESIUM which consists of zinc, magnesium and SMALL percentages of copper, silicon and iron. The percentage of zinc PRESENT is 4%.

The correct answer is (a) True

For EXPLANATION: PLASTICS are DIVIDED into two groups on the basis of their STRUCTURE – homogeneous and heterogeneous. Homogeneous plastic is made of the chain containing only carbon atoms while heterogeneous plastic consists of the chain containing carbon and oxygen, NITROGEN and other elements.