The answer is #"260 mL"#.

Usually, a #"w/v"# percent concentration is used for saline solutions, which means that a #"0.9%"# saline solution will have #"9 g"# of #"NaCl"# dissolved in enough water to make #"1000 mL"# of solution.

#"w/v" = ("mass solute")/("volume of solution") * 100#

So, if you need #"9 g"# to make #"1000 mL"# of solutions, it's clear that less #"NaCl"# will produce less #"0.9%"# solution.

#"0.9" = ("2.3 g NaCl")/("V"_("solution")) * 100 => V_("solution") = ("2.3 g" * "100")/"0.9"#

#V_("solution") = "256 mL"#, or #"260 mL"# (rounded to two sig figs).