Shyam was cooking potato curry on a chulha. To his surprise he
observed that the copper vessel was getting blackened from
outside. It may be due to:
(a) proper combustion of fuel.
(b) improper cooking of potato curry.
(c) improper combustion of the fuel.
(d) burning of copper vessel.
NCERT Class VIII
Science - Exemplar Problems
Chapter 6. Combustion and Flame