It depends on the kind of solution 20% w/w or 20% w/v. In the first case you should add 20 g of NaOH to 80 g of H2O2. In the later case you should add 20g NaOH in a volumetric flask 100ml capacity and to add water in small quantities and try to dissolve the NaOH granules. It is not so easy because the granules are coagulate and you should leave the solution apart for some time. Take care to add gradually the water till all solid is diluted and then add the last portion up the line of 100ml. This is an accurate method for preparing such solutions. Other way you could use a beaker of about 150 ml capacity and a stirrer and add water up to the line of 100ml by continuous stiring. This is not so accurate but depends on your demands.

My respect dear

it mean 20 gram of pure sodium hydroxide in 100 ml of solvent

It depends on the kind of solution 20% w/w or 20% w/v. In the first case you should add 20 g of NaOH to 80 g of H2O2. In the later case you should add 20g NaOH in a volumetric flask 100ml capacity and to add water in small quantities and try to dissolve the NaOH granules. It is not so easy because the granules are coagulate and you should leave the solution apart for some time. Take care to add gradually the water till all solid is diluted and then add the last portion up the line of 100ml. This is an accurate method for preparing such solutions. Other way you could use a beaker of about 150 ml capacity and a stirrer and add water up to the line of 100ml by continuous stiring. This is not so accurate but depends on your demands.

20% w/v NaOH are 5 mol/L, whereas 20% w/w are 6.25 mol/L. Both are relative high, but similar concentrations. I suppose you need are very basic environment and/or an excess of hydroxide ions. So, practically (in most cases) it does not matter HOW you prepare it.

But, whatever you do: Always document exactly what you did! (Maybe you have one of the cases, where it does matter!) So add the w/v or w/w to your protocol - so someone who reads it latter has not to ask :)

it`s a 20g NaOH in 100ml deionized water, you have to put the powder in a volumetric flask and then add water in small quantities till reach to the 100ml and u will have a 20% solution

Thank you all of you, for valuable suggestions :)

it is usually mean mass fraction,for that it is mean 20 g of NaOH to 80 g of H2O2.

You have to specify % in W/V or W/W. In case of former dissolve 20g NaOH in ~60 ml water in a beaker and stirred well to dissolve it. Then add Distilled water to make upto 100 ml. Since it is exothermic reaction prepare solution in beaker, once it is mixed well by stirring properly, cool it and transfer to a 100 ml volumetric flask to make up the volume to 100 ml. This solution is 20% (W/V) NaOH. In case of latter dissolve 20g NaOH in 80 g DW (i.e. 80 ml DW). Prepare solution in beaker as mentioned above.

Respected Parashuram shaoo thank you very  much

it is 20g in 100 ml water

Dear Mr. Kakarla,

If you dissolve 20g of sodium hydroxide in 100ml,  then it is of 20% NaOH and 

if 20g of NaOH in 80 ml, then it is 25% NaOH.

Please let me know if we want to make 1% NaOH solution on v/v basis, what would be ratio of salt and water?

1%NaOH neans 1g NaOH in 100 ml water since NaOH is a solid.

what we will do, if NaOH is showing humidity of 5% ????????????

bt why we are avidibg the density of NaOH , its density also play a major role .

add 20 gm in NaOH in 100 ml Standard Measuring flask & fill the water up to mark, which 20% NaOH solution.If the NaOH have 5% moisture or water content, you can increase the weight or you can calculate on dry/anhydrouse basis.

the solutions one must always refer to the total volume. in this case, 20 g of NaOH are weighed and dissolved in a volumetric flask of 100 ml in a volume of water of 60 to 70 ml. After cooling, add the amount of water to reach the 100 ml mark. you would have a 20% solution of NaOH

For analogous query, check: https://www.researchgate.net/post/How_can_i_prepare_60_NaoH_Solution