The Ka of a certain indicator is 4 ×10−7. The color of HIn is green and that of In− is red. A few drops of the indicator are added to an HCl solution, which is then titrated against an NaOH solution. Over which pH range will the indicator change color?4.4 to 6.46.4 to 8.43.4 to 5.47.4 to 9.45.4 to 7.4

pH range of indicator is 5.4 to 7.4

Explanation:

An acid-base indicator are chemical substances that change in color when pH changes.

An indicator changes in color when the pH of the solution is equal to pKa of the indicator (Where pKa is defined as - log Ka).

The pH range in which indicator changes in color is pKa ± 1.

pKa of buffer is:

- log 4x10⁻⁷ = 6.4

That means pH range of indicator is since 6.4 - 1 = 5.4 to 6.4 + 1 = 7.4.

(5.4 - 7.4)

answer:

technetium is the most reactive. this is followed by silver. the least reactive out of these three elements is strontium.

the answer is c.the valence of the atoms combine .