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Answer: (A) H₂CO₃ + HCO₃⁻ Explanation: • The bicarbonate buffer system (carbonic acid–bicarbonate) is the main physiological buffer of human blood. • It maintains pH ≈ 7.4. • Phosphate buffer (options B & D) is important in intracellular fluid and kidney. • Acetate buffer (C) is used in labs.

• “Uparikara” = an extra tax (imposed over and above regular land revenue). • Option (A): King’s share (1/6th) was called Bhaga. • Option (B): Periodic supplies = Bali or Bhoga. • Option (C): Voluntary offerings were Uparadana or Prayatna.

B

Ans C

1. Definition • Cis-polyisoprene: A polymer of isoprene in which the double bonds are arranged in the cis-configuration (H atoms on the same side). • Trans-polyisoprene: A polymer of isoprene with the trans-configuration (H atoms on opposite sides). 2. Natural Sources • Cis-polyisoprene: Found in natural rubber (from Hevea brasiliensis tree). • Trans-polyisoprene: Found in gutta-percha and balata trees. 3. Structure & Flexibility • Cis-polyisoprene: • Structure: Kinked, irregular chains due to cis arrangement. • Flexible, elastic. • Trans-polyisoprene: • Structure: More linear, closely packed. • Hard, crystalline. 4. Properties • Cis-polyisoprene (Natural Rubber): • Highly elastic (stretches and returns). • Soft at room temperature. • Poor resistance to chemicals, oxidizes easily. • Trans-polyisoprene (Gutta-percha): • Hard and tough. • Less elastic, more rigid. • Higher resistance to wear. 5. Uses • Cis-polyisoprene (Natural Rubber): Tyres, elastic bands, footwear, gloves. • Trans-polyisoprene (Gutta-percha, Balata): Golf balls, electrical insulation, surgical instruments covering, orthodontic fillings.

Ans D

BPSC PYQ 56-59 BPSC PYQ

Watson and crick — did not discovered DNA , but they discovered double helix nature of dna 🧬 in 1953 — got Nobel in 1962

Miescher - discovered DNA in 1869 itself.

Eutectic Mixture • A eutectic mixture is a mixture of two or more substances that solidify at a single sharp temperature, which is lower than the melting points of the individual components. • This temperature is called the eutectic point. • At this temperature, both (or all) components crystallize simultaneously in a fixed proportion. • It behaves like a single substance during solidification, even though it contains multiple components. Examples 1. Lead–tin alloy (used in soldering): eutectic mixture of 61.9% tin and 38.1% lead, melts at 183 °C. 2. NaCl–H₂O mixture: eutectic at –21.2 °C (used in freezing mixtures). 3. Naphthalene + Camphor mixture. Why Glass is not a eutectic mixture? • Glass does not have a sharp melting point; instead, it softens gradually. • It is an amorphous solid and best described as a supercooled liquid/solution, not a crystalline eutectic. Key Difference • Glass: amorphous, supercooled solution, no sharp melting point. • Eutectic mixture: crystalline, sharp melting point, fixed composition.