Give me two reasons that may render a metalochromic indicator efficient

A complexometric indicator is an ionochromic dye that undergoes a definite color change in presence of specific metal ions.[1] It forms a weak complex with the ions present in the solution, which has a significantly different color from the form existing outside the complex. Complexometric indicators are also known as pM indicators.[2]

the answer is a i think

it doesn't. it was imagined up in the middle ages.