UGC NTA NET/JRF Exam, Environmental Sciences, June-2025

Total Questions: 99

91. (Qs. No. 91-95): Read the following passage and answer the questions:

Hydrothermal fluids at spreading centers of Mid Oceanic Ridges originate due to circulation of sea water through hot volcanic rocks. Heated rocks and deeper magmas pull in the cold seawater, heat it and then pull out the hydrothermal fluid- the hot water.

The hydrothermal water laden with metals and many other elements returns back into the overlying oceans.

Circulating sea water through porous volcanic rocks not only cools the lithosphere but also contribute to the sea water chemistry, and formation of important mineral deposits of Co, Ni, Lanthanides and PGEs. Continental weathering also contributes to the seawater composition.

The hydrothermal energy and nutrients support complex ecosystems at Mid Oceanic Ridges. Microorganisms in the ecosystem also play important role in the precipitation of minerals.

In the year 2024, India having with two ocean probes, applied to International Sea Bed Authority under the UN Convention on the Law of the Sea (UNCLOS) to explore deep sea around Carlsberg Ridge in the north western limb of the Indian Ocean Ridge system, and Afanasy Nikitin Seamount in the Central Indian basin.

These missions can yield minerals and metals, associated with crusts and nodules, important in clean energy transition and other strategic importance.

Which of the following is mainly contributed to the sea water composition by volcanic activities?

Correct Answer: 3. CI⁻
Solution:

92. Which of the following represents steepest geothermal gradient?

Correct Answer: 3. Mid Oceanic Ridges
Solution:

• Steepest gradient: New, hot oceanic crust and high heat flow near spreading centers create the largest temperature increase per depth locally (steep geothermal gradient), despite vigorous hydrothermal circulation.

• Comparisons: Subduction forearcs are "cold" (low gradient); old/thick lithosphere has low heat flow; collision belts are warm at depth but typically have lower near-surface gradients than MORs.

93. Cobalt, Nickel and lanthanides belong to _______ .

Correct Answer: 2. Critical metals
Solution:

Grouping logic: Co (cobalt) and Ni (nickel) are key to batteries/alloys; lanthanides (REEs) are vital for magnets, electronics, catalysts. Together they're classed as critical or strategic minerals due to supply risk + economic importance.

Not rare earths (REEs) alone: Only the lanthanides are REEs; Co and Ni are not.

Not chalcophile as a set: Ni, Co are mainly siderophile/lithophile, lanthanides are lithophile.

Hydrothermal elements: Many occur in hydrothermal deposits, but that's a genetic style, not a standard category grouping these three.

94. Formation of polymetallic nodules on the surface of ocean indicates _________ .

Correct Answer: 2. oxic environment
Solution:

Nodule signal: Polymetallic (Mn-Fe) nodules form under very slow sedimentation and oxidizing bottom waters. Mn(II)→ Mn(IV) oxides and Fe oxyhydroxides scavenge Co, Ni, Cu, REES, building nodules over Myr timescales.

Anoxic settings favor sulfide formation (e.g., pyrite), not Mn-oxide nodules.

95. Carlsberg Ridge represents boundary between ________ .

Correct Answer: 3. Indian and Somalian Plates
Solution:

Plate boundary: The Carlsberg Ridge in the NW Indian Ocean is the spreading boundary between the Indian Plate and the Somali (Somalian) Plate, forming part of the Indian Ocean Ridge system.

96. (Qs. No. 96-100): Read the following passage and answer the questions:

A group of environmental toxicologists selected an endemic area in rural setting for screening females for breast cancer, based on the previous literature documentation regarding exposure to the organochlorine compound (DDT).

A total of 5000 females were screened in this activity and clinicians in the group of environmental toxicologists confirmed 250 females as positive for breast cancer.

The blood samples of 150 females were also taken to quantify the value of DDT. The mean (SD) for DDT was estimated to be normally distributed as 2.5 (1.0) ng/ml.

The epidemiologist in the team also collected detailed information regarding age of females (ranged: 15-49 years), family history (fh), type of dietary habits (vegetarian/ non-vegetarian), and menopause status (yes/no).

What is the estimated prevalence for breast cancer in the community?

Correct Answer: 4. 5%
Solution:

Prevalence = existing cases ÷ population screened = 250/5000 = 0.05 5%. Interprets the point burden of disease in this cross-section.

97. In the same community (rural area) if the prevalence of breast cancer remains the same and there is almost negligible migration, what will be the expected number of breast cancer if we assume arithmetic growth model in one year duration?

Correct Answer: 4. 262.5
Solution:

Present cases N₀ = 250.
With a 5% annual increment (as directed by the "arithmetic growth" assumption here),
N₁ = N₀(1 + 0.05) = 250 × 1.05 = 262.5.

Note: if one held prevalence strictly constant in a fixed population, the count would remain 250; this item instead asks you to apply a 5% step-up to the current case load.

98. Which test of significance should be performed to test the association between status of dietary habits and DDT levels among 150 females whose blood sample were taken?

Correct Answer: 2. One sample t test
Solution:

Two independent sample t-test

Outcome: DDT concentration (continuous; given~normal).

Grouping factor: dietary habit (vegetarian vs non-vegetarian → two independent groups).

Test: Compare two group means→ independent (two-sample) t-test (use Welch's version if variances differ).

99. Approximately for how many females, the value of DDT will be within limits of 2.5 to 3.5 ng/ml?

Correct Answer: 2. 51
Solution: