.....the Produce Index Units (PIUs) [which] is a measure of farm productivity. A tax on PIUs is, therefore, a tax on land measured not in terms of acres but in units of its quality.....

Refrence:REVENUE ESTIMATES FROM LAND TAXATION IN PAKISTAN
Page 05, 3rd Paragraph
@maryammalik

"A produce index unit reflects the “productive capacity” of land and is estimated as a measure of the gross value of produce on each unit of land by soil type. Any two acres of land located separately are assigned the same PIU if they are capable of producing about the same value of gross produce in a year. The PIUs were first established to compensate Muslim refuges for the land they had left in India after its partition in 1947. The PIUs in Pakistan were based on the revenue settlement conducted before 1947. The average PIUs per hectare is still the same in Punjab (156), Sindh (64) and NWFP (69)."

Reference: Resource Mobilization from Agriculture in Pakistan
See footnote on Page 464

Hence to me option no. "b" is correct.

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Faseeh