I do not agree with the statement.
The "substance" can be a compound. It's "pure"
as long as there's nothing else in it but its name.
'Pure' water is 100% H₂O with nothing else in it.
'Pure' table salt is 100% NaCl with nothing else in it.
'Pure' carbon dioxide is 100% CO₂ with nothing else in it.
These example substances are all compounds, not elements.
Coals energy is affordable and it is easy to burn.
Answer:
option d and b..............
Answer: For ideal machine efficiency = 1. Hence M.A = V. R. The V. R of an ideal machine and the practical machine is a constant or is the same for both
