Step 1 :Given that the half-life of the substance is 2 years, which means that in 2 years, half of the substance has decayed.
Step 2 :The formula for radioactive decay is \(N = N0 * (1/2)^{t/T}\), where \(N\) is the final amount of the substance, \(N0\) is the initial amount of the substance, \(t\) is the time elapsed, and \(T\) is the half-life of the substance.
Step 3 :We are asked to find the amount of the substance after 5 years, so we substitute the given values into the formula: \(N = 18g * (1/2)^{5/2}\)
Step 4 :Solving the equation gives us \(N = 18g * (1/2)^{2.5} = 18g * 0.17677669529663688110021109052621\)
Step 5 :Rounding to the nearest tenth of a gram, we get \(N = 3.2 g\)
Step 6 :So, after 5 years, there will be approximately \(\boxed{3.2 g}\) of the radioactive substance remaining.