Multiple choice Indol-1 is popular for beta-blocker beta blocker and calcium channel blocker pH indicator calcium indicator both (1) and (2) Reveal answer Fill a bubble to check yourself D Correct answer Explanation This option is correct because indol-1 is a popular calcium indicator similar to fura-2. In contrast to fura-2, indol-1 has a dual emission peak in Ca free solution in 475 nm while in the presence of Ca, the emission is shifted to 400 nm.