Question

Explosion limit of blast furnace gas is 37 to 71% gas in gas-air mixture. It means that the blast furnace gas will explode when burnt in a confined space, if its concentration in the gas-air mixture is _______________ percent?
A. $< 37\%$
B. $> 71\%$
C. In between $37$& $71\%$
D. None of these

Answer 1

Blast furnace gas has auto ignition point is 630-650 °C and LEL (Lower Explosive Limit) of $27\%$& UEL (Upper Explosive Limit) of 75% in an air-gas mixture at normal air pressure and temperature. It contains high concentrations of carbon monoxide which makes the gas dangerous.

Complete answer:
A. $< 37\%$
When the Explosion limit of blast furnace gas is $37$ to $71\%$ gas in gas-air mixture, then clearly the answer can’t be below 37% as mentioned in the hint.
Option A. is incorrect.
B. $> 71\%$
Similarly, When the Explosion limit of blast furnace gas is $37$ to $71\%$ gas in gas-air mixture, then again the answer can’t be above 71% as it would get out of range.
Option B. is also not correct.
C. In between $37$& $71\%$
Blast furnace Explosion limit is $37$to$71\%$ gas in gas-air mixture.
Which means that the blast furnace gas will probably explode when burnt in a confined space if the concentration in the gas-air mixture is in between $37\%$ &$71\%$.
Hence, option C is correct.
D. None of these
Option D. is again incorrect.

Additional information:
The blast furnace is a big, steel stack lined with brick refracted in nature, where iron ore, coke and limestone are dispersed into the top, and preheated air is blown into the lower part. The materials which are raw require generally $6$ to $8$ hours to drop down to the bottom of the furnace where the final product gets done which contains liquid slag and liquid iron.

Note:
Observing the question, the answer is in the question itself, Explosion limit of blast furnace is between $27\%$ to $75\%$ as auto ignition point of blast furnace is $630 - 650^\circ C$
in gas-air mixture.