Environmental Science- ICAR JRF/SRF 2024

• Scott-Sanchis (Alizarin) Method: This spectrophotometric method is standard for determining Fluoride ($\text{F}^-$) in potable water supplies.
• Reaction Mechanism: Fluoride ions react with a reddish-purple zirconium-alizarin lake complex ($\text{Zr-Alizarin}$), stripping zirconium to form a colorless complex fluoride ion ($[\text{ZrF}_6]^{2-}$). The resultant bleaching/loss of red color is proportional to the fluoride concentration.

Correct option: (1) Fluoride

• Logarithmic Decibel Addition Formula: Sound pressure levels do not add linearly. Total sound level is given by:

$$L_p = 10 \log_{10} \left( 10^{L_1/10} + 10^{L_2/10} \right)$$

• Calculation: For $L_1 = 70\text{ dB}$ and $L_2 = 80\text{ dB}$:

$$L_p = 10 \log_{10} \left( 10^7 + 10^8 \right) = 10 \log_{10} \left( 1.1 \times 10^8 \right) = 80 + 10 \log_{10}(1.1) \approx 80 + 0.41 = 80.41\text{ dB}$$

• Acoustic Rule of Thumb: When two sounds differ by $10\text{ dB}$ or more, the quieter source contributes less than $0.5\text{ dB}$, yielding a rounded level of 80 dB.

Correct option: (2) 80 dB

• Poliomyelitis $\rightarrow$ (IV) Virus: Caused by the Poliovirus (enterovirus family), an RNA virus transmitted primarily via the fecal-oral route through contaminated drinking water.
• Typhoid fever $\rightarrow$ (III) Bacteria: An acute enteric infection caused by the bacterium Salmonella enterica serovar Typhi, contracted by ingesting sewage-polluted water or food.
• Amoebic dysentery $\rightarrow$ (II) Protozoa: Caused by the parasitic amoeba Entamoeba histolytica, leading to intestinal amebiasis and ulceration.
• Hymenolepiasis $\rightarrow$ (I) Helminth: An intestinal cestode infestation caused by the dwarf tapeworm Hymenolepis nana, transmitted via ingestion of contaminated water containing oncosphere eggs.

Correct option: (1) (A) - (IV), (B) - (HIN), (C)- (H), (D) -