How can you modify the charges on two particles to quadruple the force between them without moving them? g

the charge of each particular must be doubled

Explanation:

We can solve this exercise using Coulomb's law

          F₀ = k q₁ q₂ / r²

tells us that the force is quadrupled and asks if the load

let's call the initial force F₀, let's find the force of the algae they double

                   q₁ = q₂ = 2q₀

we substitute

          F = k 2q₀o 2q₀ / r₁2

          F = 4 F₀

         we see that for the force to multiply by 4, the charge of each particular must be doubled

measuring things 1 litre of water