What is the sequence of structural genes in Lac operon?

The correct answer is Option (4) → lac z, lac y, lac a

In the lac operon of E. coli, one regulatory gene (the i gene) is followed by three structural genes that are transcribed together as one polycistronic unit. The structural genes lie in the order z, y and a, so the sequence is lac z, lac y, lac a. All three gene products are needed for the metabolism of lactose.

NCERT Extract:
The Lac Operon – “… The lac operon consists of one regulatory gene (the i gene – here the term i does not refer to inducer, rather it is derived from the word inhibitor) and three structural genes (z, y, and a). The i gene codes for the repressor of the lac operon. The z gene codes for beta-galactosidase (β-gal), which is primarily responsible for the hydrolysis of the disaccharide, lactose into its monomeric units, galactose and glucose. The y gene codes for permease, which increases permeability of the cell to β-galactosides. The a gene encodes a transacetylase.”