A particular thermal system involves three objects of fixed shape with conduction resistances of R₁ = 1 K/W, R₂ = 2 K/W and R₃ = 4 K/W, respectively. An objective is to minimize the total thermal resistance R_tot associated with a combination of R₁, R₂, and R₃. The chief engineer is willing to invest limited funds to specify an alternative material for just one of the three objects; the alternative material will have a thermal conductivity that is twice its nominal value. Which object (1, 2, or 3) should be fabricated of the higher thermal conductivity material to most significantly decrease R_tot?