A chromate 𝐶𝑟𝑂4 −2 solution has an absorbance of 1.534 when the cell length is 1.5 cm. If the molar absorptivity of chromate ion is 5.21 × 103 𝑀−1 𝑐𝑚−1 , calculate the concentration of chromate ion.

Answer 1

I don't know your problem here but it appears to me to be a plug and chug problem.
A = abc
A = 1.534
a = 5210
b = 1.5
c = ?
Substitute and solve for c. The units for c will be mols/L since a is the molar absorptivity constant.

Answer 2

thank you dr bob, i get the answer.