Assume that the de Broglie wave associated with an electron can form a standing wave between the atoms arranged in a one dimensional array with nodes at each of the atomic sites. It is found that one such standing wave is formed if the distance d between the atoms of the array is \[2\overset{\text{o}}{\mathop{\text{A}}}\,\]A similar standing wave is again formed if d is increased to \[2.5\overset{\text{o}}{\mathop{\text{A}}}\,\]but not for any intermediate value of d. The energy of the electrons in electron volt and the least value of d for which the standing wave of the type described above can form, respectively are

• A. 112eV, \[1.5\overset{\text{o}}{\mathop{\text{A}}}\,\]  
• B. 151eV, \[0.5\overset{\text{o}}{\mathop{\text{A}}}\,\]
• C. 211eV, \[1.5\overset{\text{o}}{\mathop{\text{A}}}\,\]
• D. None of these