To solve this problem, we need to determine the electronic configurations of europium (Eu), gadolinium (Gd), and terbium (Tb).$\newline$The atomic numbers are given as follows:$\newline$• Eu (Atomic No. 63)$\newline$• Gd (Atomic No. 64)$\newline$• Tb (Atomic No. 65)$\newline$Let's analyze the electronic configurations step-by-step:$\newline \newline$1. Europium (Eu, Atomic No. 63):$\newline$• The configuration of xenon (Xe, Atomic No. 54) is: $[Xe] = 1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 5s^2 5p^6 \newline$• After Xe, we fill the 4f and 6s orbitals:$\newline$• Eu has 9 more electrons to distribute: $4f^7 6s^2 \newline$• Therefore, the configuration is: $[Xe]4f^7 6s^2 \newline \newline$2. Gadolinium (Gd, Atomic No. 64):$\newline$• Following Eu, Gd has one more electron:$\newline$• The electron enters the 5d orbital to minimize energy: $4f^7 5d^1 6s^2 \newline$• Therefore, the configuration is: $[Xe]4f^7 5d^1 6s^2 \newline \newline$3. Terbium (Tb, Atomic No. 65):$\newline$• Following Gd, Tb has one more electron:$\newline$• The electron enters the 4f orbital: $4f^9 6s^2 \newline$• Therefore, the configuration is: $[Xe]4f^9 6s^2 \newline \newline$Analyzing the options:$\newline$• Option 1: Incorrect configuration for Gd and Tb.$\newline$• Option 2: Incorrect configuration for Eu and Tb.$\newline$• Option 3: Incorrect configuration for Eu and Tb.$\newline$• Option 4: Correct configurations for Eu, Gd, and Tb.$\newline$Therefore, the correct option is Option 4.