The reason for choosing option (2) to complete the sentence is as follows:

- The sentence is describing two actions happening simultaneously in the past. Sarakshi was playing in the park, and her mother called her during this time.

- The correct past tense form for "is playing" is "was playing" to indicate an ongoing action in the past.

- "Called" is the appropriate past tense form for the second action, as it indicates that the action of calling Sarakshi occurred while she was playing in the park.

- Options (1), (3), and (4) do not use the correct past tense forms or verb forms to maintain the past tense and the concurrent nature of the actions, making option (2) the correct choice.