Choose the appropriate idiom to replace the underlined part of sentence.

He has taken his loss so seriously that he fell sick.

taken to heart

The correct answer is Option (1) - taken to heart

The phrase "taken his loss so seriously" suggests that he was deeply affected by the loss.

• "Taken to heart" means to be deeply affected or upset by something, which fits perfectly in the sentence.
• Corrected sentence:
  "He has taken his loss to heart so seriously that he fell sick."

OTHER OPTIONS

• "Take the bull by its horns"  (Means to face a difficult situation boldly, which doesn't fit the context.)
• "Put in his mind"  (Not a correct idiom in this context.)
• "Taken off and on"  (Incorrect phrase; "off and on" means occasionally, which is irrelevant here.)