Questions

The multiplier effect means that "An effect in economics in which an increase in spending produces an increase in national income and consumption greater than the initial amount spent."

The trick here is to follow the structure of the statement. The blank is followed by 'of' and thus the blank will take a filler that can be followed grammatically by 'of' and also manages to give a proper meaning. On the basis of these filters, none of the options except option 2 makes any sense.

The Sales Order is a confirmation document sent to the customers before delivering the goods or services. 

Sales Order (SO) can be created once the quote is accepted by your prospective customer and the Purchase Order (PO) is sent by the customer for further processing.

Pitt's India Act (1858)

A hard copy of a document is a physical object which is printed on printer.