Decimolar solution is a standard solution
The solution whose strength is known accurately is called standard solution. Again decimolar solution is that solution when one tenth mole of a solute remains in one litre solution that means the strength of decimolar solution is known. So decimolar solution is called a standard solution.
e.g: 0.1 M NaOH solution means that the strength of NaOH is 0.1M which is known. So, 0.1 M NaOH solutions is standard solution.