The 0.05 moles of 
required to make 1 L of solution in which the 
concentration is 0. 15 M.
Calculation,
The Sodium phosphate dissolves as follows:
→ 
To make 1. L of solution in which the 
concentration is 0. 15 M
The morality of = 0.15 M = number of moles / volume in lit
The morality of = 0.15 M = number of moles /1 Lit
number of moles of = 0.15 mole
The mole ratio is 1: 3
It means, the 1 mole of required to form 3 mole of
So, to form 0.15 mole of = 1×0.15 / 3 moles of required.
Hence, number of moles of required = 0.05 moles.
learn about moles
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Its just called a test tube holder
