Step 1: Break the sentence into parts.
The sentence is 'The shopkeeper sells lemons.'
It has three main parts: a subject, a verb, and an object.
Step 2: Use the question test to find each part.
Ask "who sells?" The answer is "the shopkeeper", so that is the subject.
Ask "sells what?" The answer is "lemons", so that word answers the "what" question after the verb.
Step 3: Match this to the grammar rule.
A word that answers "what" or "whom" after the verb is called the object of the verb.
Since 'lemons' answers "sells what?", it takes the object position in the sentence.
Step 4: Rule out the other labels.
'Lemons' is not doing the selling, so it is not the subject.
It is not an action word like 'sells', so it is not the verb, and it is only one word, not the full phrase 'sells lemons', so it is not the predicate.
Final Answer:
The word 'lemons' completes the action started by the verb, so it is the object.
\[ \boxed{\text{object}} \]