The wavelength of most energetic X-rays emitted when a metal target is bombarded by 40KeV electrons, is approximately (\[h=6.62\times {{10}^{-34}}\] J-sec; 1 eV = \[1.6\times {{10}^{-19}}\]J; c = \[3\times {{10}^{8}}\,m/s)\] [MNR 1991; MP PMT 1999; UPSEAT 2000; Pb. PET 2004]

• A. 300 Å
• B. 10 Å
• C. 4 Å
• D. 0.31 Å