You can choose, a set (6chips CYMK WW ), two chips(white cartrediges) , or 1 chip for individual white cartredige. 
6-chips:
* compatible Epson C13T72510N black ink cartridge
* compatible Epson C13T72520N cyan ink cartridge
* compatible Epson C13T72530N magenta ink cartridge
* compatible Epson C13T72540N yellow ink cartridge
* 2x compatible Epson C13T725A0N white ink cartridge (A1 and A2)
 
Or:
A1, A2
A1, A1
A2, A2
A1
A2
 
This note is only about the two white ink cartrediges;  
Most of the time, your printer will work with these cartridges with the default combination (A1; A2). Although it is not common, some printers have been known to reject one of these chips. In this case, they will  function with another combination, either (A1; A1), or (A2; A2).
If this is the first time you are using refillable cartridges, start with the default combination (A1; A2). If this does not work (which is rare), you can purchase an A1 chip or an A2 chip separately.
 
Please not:
- "one-time chip," it means that the chip can only be used for a single reset or refill operation. After this operation when the ink starts to run out, the chip becomes inactive or unusable, it is necessary to replace the chip, and then refill the cartridges for futher use.