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Past Questions — 2026
In a sedimentation tank, detention time is provided for:
A)
Disinfection
B)
Filtration
C)
Settling of suspended particles
D)
Aeration
Option C is correct: Settling of suspended particles.
Turbidity in water is mainly caused by:
A)
Dissolved gases
B)
Suspended particles
C)
Hardness
D)
Chlorides
Option B is correct: Suspended particles.
Which demand is considered while designing fire hydrant systems?
A)
Industrial demand
B)
Commercial demand
C)
Fire demand
D)
Institutional demand
Option C is correct: Fire demand.
The arithmetic increase method of population forecasting assumes:
A)
Constant percentage growth
B)
Sudden growth
C)
Constant numerical increase
D)
Negative growth
Option C is correct: Constant numerical increase.
Biogas plants mainly produce:
A)
Oxygen
B)
Nitrogen
C)
Carbon monoxide
D)
Methane gas
Option D is correct: Methane gas.
Rainwater harvesting primarily aims to:
A)
Increase wastewater generation
B)
Conserve water resources
C)
Increase runoff
D)
Reduce evaporation
Option B is correct: Conserve water resources.
Diseases transmitted through insects are called:
A)
Water-borne diseases
B)
Air-borne diseases
C)
Vector-borne diseases
D)
Food poisoning
Option C is correct: Vector-borne diseases.
Ventilation pipe in a water tank is provided to:
A)
Drain water
B)
Increase pressure
C)
Allow air circulation
D)
Remove sludge
Option C is correct: Allow air circulation.
Controlled tipping is also known as:
A)
Incineration
B)
Composting
C)
Sanitary landfill
D)
Pulverization
Option C is correct: Sanitary landfill.
Which ingredient in concrete acts as a binding material?
A)
Sand
B)
Aggregate
C)
Water
D)
Cement
Option D is correct: Cement.
Segregation in concrete means:
A)
Proper mixing
B)
Increase in workability
C)
Separation of coarse aggregate from mortar
D)
Reduction in cement content
Option C is correct: Separation of coarse aggregate from mortar.
Which chemical is commonly used for disinfection of drinking water?
A)
Alum
B)
Lime
C)
Potassium permanganate
D)
Chlorine
Option D is correct: Chlorine.
HDPE pipes are preferred because they are:
A)
Corrosion resistant
B)
Brittle
C)
Heavy
D)
Expensive
Option A is correct: Corrosion resistant.
The Mizoram Water Supply (Control) Act mainly regulates:
A)
Road construction
B)
Forest management
C)
Electricity supply
D)
Water supply and distribution
Option D is correct: Water supply and distribution.
Which type of cement gains strength rapidly?
A)
Low heat cement
B)
Sulphate resisting cement
C)
Rapid hardening cement
D)
White cement
Option C is correct: Rapid hardening cement.
The most suitable pump for deep bore wells is:
A)
Centrifugal pump
B)
Reciprocating pump
C)
Submersible pump
D)
Air lift pump
Option C is correct: Submersible pump.
GI pipe stands for:
A)
Galvanized Iron
B)
Ground Iron
C)
General Iron
D)
Grey Iron
Option A is correct: Galvanized Iron.
Honeycombing in concrete occurs due to:
A)
Excess curing
B)
Excess cement
C)
Poor compaction
D)
Low temperature
Option C is correct: Poor compaction.
The minimum clear cover in RCC protects reinforcement from:
A)
Expansion only
B)
Corrosion and fire
C)
Settlement
D)
Vibration
Option B is correct: Corrosion and fire.
Which material is commonly used for masonry work?
A)
Concrete
B)
Brick
C)
Steel
D)
Aluminium
Masonry is defined as the building of structures from individual units, which are often laid in and bound together by mortar.
1. **Brick (Option b):** Bricks are the most common and traditional units used in masonry work (Brick Masonry). Other common masonry units include stone, concrete blocks, and adobe. Therefore, this is the correct answer.
2. **Concrete (Option a):** While concrete is used in 'concrete masonry units' (CMUs), concrete itself is typically categorized as a cast-in-place material or a composite material rather than a masonry unit. Masonry refers to the assembly of discrete units.
3. **Steel (Option c):** Steel is a structural metal used for framing, reinforcement, or cladding, but it is not a masonry material.
4. **Aluminium (Option d):** Aluminium is a non-ferrous metal used for window frames, doors, and cladding, but it cannot be used for masonry work.
Which chemical is commonly used for water disinfection?
A)
Alum
B)
Lime
C)
Chlorine
D)
Soda
Step-by-step reasoning:
1. **Disinfection** is the process of killing pathogenic microorganisms (bacteria, viruses, and protozoa) in water to make it safe for human consumption.
2. **Chlorine (Option c)** is the most widely used chemical for disinfection globally. It acts as a powerful oxidizing agent that penetrates the cell walls of microorganisms, disrupting their enzymatic activity and killing them. It also provides a 'residual effect,' meaning it continues to protect the water from re-contamination as it travels through the distribution system.
3. **Alum (Option a)**, or Aluminum Sulfate, is used as a 'coagulant' in water treatment. It helps in removing turbidity by clumping small particles together into larger flocs, but it does not disinfect the water.
4. **Lime (Option b)**, or Calcium Hydroxide, is primarily used for 'water softening' (removing hardness) and pH adjustment to prevent corrosion in pipes.
5. **Soda (Option d)**, usually referring to Soda Ash (Sodium Carbonate), is also used for water softening and pH stabilization, not for disinfection.
Which concrete grade is minimum for RCC work?
A)
M10
B)
M15
C)
M20
D)
M25
According to IS 456:2000 (the Indian Standard code of practice for Plain and Reinforced Concrete), the minimum grade of concrete for Reinforced Cement Concrete (RCC) work depends on the exposure conditions. For 'Mild' exposure conditions, the minimum grade of concrete specified for RCC is M20. Grades below M20 (such as M10 and M15) are generally used for Plain Cement Concrete (PCC) or lean concrete work and are not permitted for structural RCC elements because they do not provide sufficient strength and durability to protect the reinforcement from corrosion. While higher grades like M25 are used for more severe exposure conditions, M20 remains the absolute baseline minimum for any RCC work under standard conditions.
Pump efficiency is ratio of:
A)
Output heat/Input heat
B)
Output discharge/Input discharge
C)
Output power/Input power
D)
Output head/pipe length
Pump efficiency (η) is a measure of how effectively a pump converts mechanical energy (input) into hydraulic energy (output).
1. **Water Power (Output Power):** This is the useful power delivered to the fluid, calculated as P_out = ρ × g × Q × H (where ρ is density, g is gravity, Q is discharge, and H is head).
2. **Brake Power (Input Power):** This is the power supplied to the pump shaft by the motor or engine (P_in).
3. **Efficiency Formula:** Efficiency is defined as the ratio of the useful power output to the total power input: η = (Output Power / Input Power) × 100%.
Why other options are incorrect:
- Option (a): Pumps are mechanical devices for moving fluids, not heat exchangers; heat is a loss (inefficiency), not the intended output.
- Option (b): Discharge is the volume flow rate. Input and output discharge are generally the same (minus leaks), and their ratio does not define efficiency.
- Option (d): Head is a measure of pressure/height, and pipe length is a physical dimension; their ratio is not a measure of efficiency.
GI pipes are mainly:
A)
Plastic pipes
B)
Galvanized Iron pipes
C)
Cement pipes
D)
Copper pipes
The term 'GI' is a standard engineering abbreviation for 'Galvanized Iron'. Galvanization is the process of applying a protective zinc coating to iron or steel to prevent rusting and corrosion. In piping materials, GI pipes are widely used for water supply and plumbing due to their strength and corrosion resistance.
Analysis of other options:
- Option (a) Plastic pipes: These include materials like PVC, HDPE, or CPVC, which are polymers, not iron.
- Option (c) Cement pipes: These are made from concrete or asbestos-cement and are typically used for sewage or large-scale water mains.
- Option (d) Copper pipes: These are made from pure copper and are distinct from iron-based materials.
Circular water tanks are preferred because they:
A)
are cheaper
B)
are taller
C)
distribute pressure uniformly
D)
need less concrete
In a circular water tank, the water exerts hydrostatic pressure equally in all radial directions. This results in 'hoop tension' (circumferential stress) acting uniformly around the perimeter of the wall. Because the geometry is symmetrical, there are no corners or edges where stress concentrations occur, unlike in rectangular tanks where the corners are subject to high bending moments and stress concentrations. This uniform distribution of pressure allows the structure to be more stable and efficient in resisting the outward force of the stored liquid.
Regarding other options:
- (a) and (d): While circular tanks can be more material-efficient for a given volume, they are not always 'cheaper' or requiring 'less concrete' in every construction context due to the complexity of circular formwork compared to straight formwork.
- (b): Height is a design choice based on capacity and site requirements, not a inherent reason why circular shapes are preferred over rectangular ones.