How we decide address bit to select bit from one row?

Question

It is given that for 4096 cells in each row are divided in to 512 groups of 8. Therefore address bits are of 12 to select row and 9 are to select a bit from a selected row.

My question is how we decide this 9 bits for one row in order to select one bit ?

Comments

Those 9 bits are for selection of one Byte in a Byte addressable machine only

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4096 cells for all rows and 512 rows with 8 Bit(byte) in one row that's why we are selecting each row with 12 bits of address (higher order) and 9 bits(lower order) to specify one bit from required row. To make it total 21 bit address as it is memory is of 16 megabit I.e. 2M*8.