Electrical behavior of refractories for electric furnaces: identify the statement that is incorrect for materials used in such electrically heated equipment.

Introduction / Context:
Electric furnaces rely on controlled current paths and precise thermal input. The electrical properties of refractories matter because unintended conduction can cause hot spots, short circuits, or energy losses. This item asks you to find the wrong statement regarding electrical behavior of refractory linings in electric furnaces.

Given Data / Assumptions:

• Electric furnaces require linings that minimise parasitic current flow.
• Many oxide refractories are effective electrical insulators at moderate temperatures.
• Graphite and metallic refractories are conductive.

Concept / Approach:
When a refractory lines an electric furnace, its bulk resistivity influences safety and efficiency. In most cases, low electrical conductivity (high resistivity) is desirable to confine current to the designed elements/electrodes. Porosity further interrupts conduction paths, generally lowering effective conductivity. Statements that downplay the importance of conductivity in electric furnaces are therefore incorrect.

Step-by-Step Solution:
Check each choice against practical requirements for electric furnaces.(a) claims conductivity is unimportant; this contradicts design practice.(b) is broadly correct: graphite/metals are conductive; most oxide bricks are insulating.(c) is correct: low-conductivity linings are ordinarily preferred.(d) is correct: porosity tends to lower conductivity.

Verification / Alternative check:
Electrical resistivity data for fireclay, alumina, magnesia, and silica show high resistivity compared with graphite. Electric-arc and resistance furnace linings are chosen accordingly.

Why Other Options Are Wrong/Right:
(a) Wrong — conductivity matters greatly for electric furnaces.(b), (c), (d) — in line with standard refractory selection guidelines.

Common Pitfalls:
Overlooking temperature dependence of resistivity; some oxides become more conductive at very high temperatures and must be evaluated in their service window.

Final Answer:
Electrical conductivity of refractory is not important, when these are to be used in electrical furnaces.