For a spark ignition engine, the equivalence ratio (f) of mixture entering the combustion chamber has values.

Question

For a spark ignition engine, the equivalence ratio ($\phi$) of mixture entering the combustion chamber has values.                                                                                                               

      (a) $\phi$ < 1 for idling and $\phi$ > 1 for peak power conditions.

      (b) $\phi$ > 1 for both idling and peak power conditions

      (c) $\phi$ > 1 for idling and $\phi$ < 1 for peak power conditions

      (d) $\phi$ < 1 for both idling and peak power conditions.