Hello Aman,

Here is the solution -

A 6.90M solution contains 6.90 mol KOH in 1000 cm3 of the solution -

Mass of 6.90 mol of KOH = 6.90×56 = 386.4g

A 30% solution contains 30g of KOH present in 100g of the solution -

So, 386.4 g of KOH is present in = 100×386.430 = 1288g of solution

Hence, the density of KOH solution = Mass / Volume

= 1288g1000cm3

= 1.288gcm−3