The $X$-ray wavelength of $L_a$ line of platinum $(Z = 78)$ is $1.30 \mathring{A}$. The $X$-ray wavelenght of $L_a$ line of molybdenum $(Z =42)$ is :

Question

( A ) 2.70 \mathring{A}$
( B ) $5.41 \mathring{A}$
( C ) $1.35 \mathring{A}$
( D ) $4.59 \mathring{A}$