Thermodynamics, Energy & Mechanics

Correct matching pairs: (A) Solar energy matches with (IV) Water pumping (solar photovoltaic water pumping systems). (B) Gasification matches with (I) Biomass (thermochemical gasification of solid biomass into producer gas). (C) Fuel cell matches with (II) Chemical energy (electrochemical device converting chemical energy directly to electricity). (D) Fixed dome matches with (III) Biogas (Janata/Deenabandhu fixed-dome biogas plant). Option analysis: (A) Incorrect matching. (B) Incorrect matching. (C) Incorrect matching. (D) (A)-(IV), (B)-(I), (C)-(II), (D)-(III) is the exact match.

The global planetary albedo of the Earth is approximately $0.30$ or $30\%$, meaning roughly $30\%$ of incoming solar radiation is scattered and reflected back to space by clouds, atmospheric aerosols, and reflective land/ice surfaces without heating the Earth system. Option analysis: (A) $10\%$ is far too low. (B) $20\%$ is too low. (C) $30\%$ represents the standard Earth planetary albedo. (D) $40\%$ is too high.

Biogas produced from anaerobic digestion of organic wastes consists primarily of Methane ($\text{CH}_4$, $55\text{--}70\%$) and Carbon Dioxide ($\text{CO}_2$, $30\text{--}45\%$), with traces of hydrogen sulfide, water vapor, and nitrogen. Option analysis: (A) Biogas is produced under strict anaerobic conditions, so free oxygen is absent. (B) Lacks combustible methane. (C) Methane and carbon-dioxide comprise over $95\%$ of biogas volume. (D) Carbon monoxide is present in producer gas, not biogas.