Answer
Nickel.
Work Step by Step
Apply equation 41.48, relating the x-ray energy to Z.
$$E_{K_\alpha}=(Z-1)^2(10.2\;eV)$$
$$7460eV=(Z-1)^2(10.2\;eV)$$
$$Z=1+\sqrt{\frac{7460\;eV }{10.2\;eV}}\approx 28$$
The element is nickel.
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