Groundwater Chemistry Questions and Answers

Q: 'Fluorosis' is the disease caused due to contamination of water by :

Fluorosis is caused by fluoride in drinking water.Drinking water with fluoride above about 1.5 mg/L over long periods causes dental fluorosis, with mottled and stained teeth, and at higher levels skeletal fluorosis, with stiff, painful joints and bone deformities. Fluoride-bearing minerals such as fluorite and fluorapatite in granites and gneisses release it to groundwater, a problem in Rajasthan, Andhra Pradesh, Telangana and other states.Arsenic causes arsenicosis, high nitrate causes methaemoglobinaemia (blue baby syndrome), and sulphate mainly gives a laxative effect and bitter taste. None of them causes fluorosis.

Q: The groundwater in the Narmada valley and the hilly terrain in western and central India falls is this category of major hydrogeochemical provinces of India :

The answer given is the Bicarbonate Province.India's groundwater is grouped into hydrogeochemical provinces by the dominant anion. The Narmada valley and the basaltic and crystalline hills of western and central India are places where water meets silicate rocks (Deccan basalt, Archaean crystalline rocks and alluvium), and groundwater there is typically of the calcium-magnesium bicarbonate kind. A 2023 study of 305 groundwater stations in the Narmada basin found bicarbonate to be the dominant anion throughout the basin, with calcium dominant among cations in the upper and middle basin.The chloride and the mixed bicarbonate-chloride provinces correspond to areas where sodium chloride salts are important, such as arid, coastal or saline-affected tracts, which is not the character of this valley.What could not be confirmed is the formal province map itself: no source found names the province boundaries, so the match with the key rests on the dominance of bicarbonate in the valley's groundwater.

Q: The value of SAR is used in classifying the water for :

SAR is used to classify water for Irrigation use.The sodium adsorption ratio compares sodium with calcium and magnesium in water:\[ \mathrm{SAR} = \frac{Na}{\sqrt{(Ca + Mg)/2}} \](concentrations in meq/L). Water with a high SAR makes sodium replace calcium and magnesium on clay particles, which disperses the clay and destroys soil structure and permeability. The US Salinity Laboratory diagram classifies irrigation water by SAR together with electrical conductivity.Drinking water and industrial water are judged by other standards, such as total dissolved solids, hardness and specific ions, so domestic, industrial, and '(A) and (B)' are wrong.

Q: The hardness in water is typically caused by the presence of :

Hardness is caused by calcium and magnesium ions.Hard water contains dissolved Ca2+ and Mg2+ picked up from limestone, dolomite and gypsum. These ions react with soap to form scum instead of lather, and when the water is heated they precipitate as scale. Hardness is expressed as mg/L of CaCO3.Carbonate and bicarbonate ions are the anions that make part of the hardness 'temporary' (removable by boiling), but the hardness itself is due to the cations. Sodium and potassium are monovalent and do not cause hardness. Suspended matter causes turbidity, not hardness.

Q: Consumption (drinking) of water with high concentration of nitrates causes :

High nitrate in drinking water causes blue baby syndrome, methaemoglobinaemia.In infants, nitrate is reduced to nitrite in the gut. Nitrite oxidises haemoglobin to methaemoglobin, which cannot carry oxygen, so the baby's skin turns bluish. That is why the BIS limit for nitrate in drinking water is 45 mg/L. Nitrate in groundwater comes mainly from fertilisers, sewage and animal waste.Knock-knee and skeletal fluorosis are caused by excess fluoride. Blackfoot disease, a gangrene of the feet, is linked with chronic arsenic poisoning, as in Taiwan.

'Fluorosis' is the disease caused due to contamination of water by :

A.Arsenic
B.Fluoride
C.Nitrate
D.Sulphate

Exam Year(s)

MH SET - 2018, SET Exam - 2018,

Answer: B

Fluorosis is caused by fluoride in drinking water.

Drinking water with fluoride above about 1.5 mg/L over long periods causes dental fluorosis, with mottled and stained teeth, and at higher levels skeletal fluorosis, with stiff, painful joints and bone deformities. Fluoride-bearing minerals such as fluorite and fluorapatite in granites and gneisses release it to groundwater, a problem in Rajasthan, Andhra Pradesh, Telangana and other states.

Arsenic causes arsenicosis, high nitrate causes methaemoglobinaemia (blue baby syndrome), and sulphate mainly gives a laxative effect and bitter taste. None of them causes fluorosis.

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The groundwater in the Narmada valley and the hilly terrain in western and central India falls is this category of major hydrogeochemical provinces of India :

A.Bicarbonate Province
B.Bicarbonate-Chloride Province
C.Chloride Province
D.Bicarbonate-Chloride and Chloride Province

Exam Year(s)

MH SET - 2019, SET Exam - 2019,

Answer: A

The answer given is the Bicarbonate Province.

India's groundwater is grouped into hydrogeochemical provinces by the dominant anion. The Narmada valley and the basaltic and crystalline hills of western and central India are places where water meets silicate rocks (Deccan basalt, Archaean crystalline rocks and alluvium), and groundwater there is typically of the calcium-magnesium bicarbonate kind. A 2023 study of 305 groundwater stations in the Narmada basin found bicarbonate to be the dominant anion throughout the basin, with calcium dominant among cations in the upper and middle basin.

The chloride and the mixed bicarbonate-chloride provinces correspond to areas where sodium chloride salts are important, such as arid, coastal or saline-affected tracts, which is not the character of this valley.

What could not be confirmed is the formal province map itself: no source found names the province boundaries, so the match with the key rests on the dominance of bicarbonate in the valley's groundwater.

Discuss in Forum

The value of SAR is used in classifying the water for :

A.Domestic use
B.Irrigation use
C.Industrial use
D.(A) and (B)

Exam Year(s)

MH SET - 2023, SET Exam - 2023,

Answer: B

SAR is used to classify water for Irrigation use.

The sodium adsorption ratio compares sodium with calcium and magnesium in water:

\[ \mathrm{SAR} = \frac{Na}{\sqrt{(Ca + Mg)/2}} \]

(concentrations in meq/L). Water with a high SAR makes sodium replace calcium and magnesium on clay particles, which disperses the clay and destroys soil structure and permeability. The US Salinity Laboratory diagram classifies irrigation water by SAR together with electrical conductivity.

Drinking water and industrial water are judged by other standards, such as total dissolved solids, hardness and specific ions, so domestic, industrial, and '(A) and (B)' are wrong.

Discuss in Forum

The hardness in water is typically caused by the presence of :

A.Sodium and potassium ions
B.Suspended matter
C.Carbonate and bicarbonate ions
D.Calcium and magnesium ions

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: D

Hardness is caused by calcium and magnesium ions.

Hard water contains dissolved Ca²⁺ and Mg²⁺ picked up from limestone, dolomite and gypsum. These ions react with soap to form scum instead of lather, and when the water is heated they precipitate as scale. Hardness is expressed as mg/L of CaCO₃.

Carbonate and bicarbonate ions are the anions that make part of the hardness 'temporary' (removable by boiling), but the hardness itself is due to the cations. Sodium and potassium are monovalent and do not cause hardness. Suspended matter causes turbidity, not hardness.

Discuss in Forum

Consumption (drinking) of water with high concentration of nitrates causes :

A.Knock knee syndrome
B.Skeletal fluorosis
C.Black foot disease
D.Blue baby syndrome

Exam Year(s)

MH SET - 2025, SET Exam - 2025,

Answer: D

High nitrate in drinking water causes blue baby syndrome, methaemoglobinaemia.

In infants, nitrate is reduced to nitrite in the gut. Nitrite oxidises haemoglobin to methaemoglobin, which cannot carry oxygen, so the baby's skin turns bluish. That is why the BIS limit for nitrate in drinking water is 45 mg/L. Nitrate in groundwater comes mainly from fertilisers, sewage and animal waste.

Knock-knee and skeletal fluorosis are caused by excess fluoride. Blackfoot disease, a gangrene of the feet, is linked with chronic arsenic poisoning, as in Taiwan.

Discuss in Forum

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