Phosphoric acid manufacturing routes: Compared with the wet process, which statement correctly characterizes the electric (thermal) process for manufacturing phosphoric acid?

Introduction / Context:
Two major industrial routes produce phosphoric acid: the wet process (acidulation of phosphate rock with sulphuric acid) and the electric/thermal process (production of elemental phosphorus in an electric furnace, oxidation to P2O5, and hydration to H3PO4). Understanding key differences guides process selection for fertilizer vs. high-purity acid markets.

Given Data / Assumptions:

• Wet process yields ordinary (merchant-grade) acid with gypsum byproduct.
• Thermal process yields high-purity, stronger acid and is capital/energy intensive.
• Single best statement is required.

Concept / Approach:
The electric (thermal) route is less common because it consumes more power and requires high-grade rock and coke/silica in a furnace. It does not generate gypsum; that byproduct arises in the wet process. The thermal route directly makes stronger, purer acid preferred for specialty uses (food, electronics), whereas wet process acid is often concentrated and purified for fertilizers.

Step-by-Step Solution:
Identify attributes: less frequent industrial use; high-purity product; no gypsum.Match to options: only option (a) captures these facts succinctly.Eliminate the remaining distractors accordingly.

Verification / Alternative check:
Process flow diagrams and industry references distinguish wet-process acid (with CaSO4 byproduct) from thermal acid (no gypsum, higher purity), confirming the selection.

Why Other Options Are Wrong:
(b) Opposite of reality; thermal route prefers higher-grade rock.

(c) Gypsum is a wet-process byproduct, not from the electric route.

(d) Thermal route yields strong acid; wet is initially weaker/dilute.

Common Pitfalls:

• Confusing wet-process (gypsum) with thermal (no gypsum).
• Assuming frequent use; thermal is niche due to cost.

Final Answer:
It is used less frequently and produces strong acid without a gypsum byproduct.