Given data
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Energy(E)=9.00*10^(-19)
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We know(E)=hf  ( f=c/lamda)
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So     E=hc/lamda
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Lamda =hc/E
                             =(6.63)*^10(-34)*(3)*10(^8)/(9.00)*10^(-19)
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=(6.63)*(3)*(10)^(-26)(/9.00)*(10)^(-19)
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=(19.89/9.00)*10(-7)
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=2.21*10(-7) meters
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=221 nm