Explanation: The economical spacing of roof trusses works out to be 1/3 to 1/5 of the span. A structure that is composed of a number of line numbers connected at the ends to form a triangulated framework is called a truss.

Explanation: The top chord members of roof truss are called principal rafters. They support the roof covering through purlins. They are mainly compression members.

Explanation: The bottom chord member of the truss is known as the main tie. It is usually in tension and takes compression if reversal of loads occurs due to wind load intensity.

iii. Wind load.

Explanation: Pitch of roof truss is defined as the ratio of rise to the span of a truss. It should be 1/6 for G I sheets, 1/12 for AC sheets and ¼ when snow load occurs besides wind load.

Explanation: Angle of repose is defined as the maximum natural slope at which the soil particles will rest due to internal friction if left unsupported for long time. Angle of repose of soil depends on its nature and moisture content. For water, the angle of repose is zero.

Explanation: The water should be free from BOD to ensure it as fit for drinking. According to standards of potable water, free ammonia should not be more than 0.15 ppm and nitrites should not be more than 20 ppm.

Explanation: The substance which is used for coagulation is known as a coagulant. Alum has proved to be an effective covalent and it is widely used the coagulant is effective between pH range of 6.5 to 8.5.

Explanation: When coagulants are dissolved in water, they produce thick gelatinous precipitates. This precipitate is known as floc and the process is known as flocculation. The floc is heavy and hence it starts to settle down at the bottom of the tank.

Explanation: Aeration is a method by which water is brought in close contact air so as to absorb oxygen for the reduction of taste, odour etc. by virtue of oxidation.

Explanation: Usage of the cascade is a method of aeration, in which the water is allowed to fall over a series of concrete steps. During the fall, the water gets thoroughly mixed with the atmospheric air and gets aerated.

Explanation: Use of chloramine is a method of disinfection. It is found that chlorine alone is not stable in water but when it is mixed in water with ammonia, it forms compounds known as chloramines. These are very effective in killing bacteria.

• It is denoted by “k”.

Explanation: The stress corresponding to 0.2% of strain in the stress-strain curve of mild steel is known as proof stress and this also taken as yield stress. The maximum stress is generally taken as yield stress.