Among the sources of energy listed below, which one is nonconventional in present day rural India?

Answer: (c) Biogas

Biogas was a non-conventional (new) source in rural India.

The idea

Biogas forms when microbes break down organic waste without oxygen. The gas is collected for fuel instead of burning the raw waste directly. “Non-conventional” here describes the energy method in the 1988 rural context, not whether the raw material was newly discovered.

Dung and water enter a digester → Oxygen is excluded → Microbes break down organic matter → Methane-rich gas collects → Gas is used for cooking or other energy → Digested slurry is removed

Why the others are wrong

(a) Firewood is traditional.

(b) Dung cakes are traditional.

(d) Hydel is conventional.

The trap

Dung is used in both — burnt as cakes (traditional) or digested for biogas (new).

Also know

Biogas contains mainly methane and carbon dioxide; the leftover slurry can be used as manure. Biomass is the wider category and includes wood, crop waste and dung. Gasification uses limited oxygen at high temperature, whereas a biogas digester uses microbial action without oxygen.