A) 144
B) 143
C) 142
D) 146
Correct Answer: B
Solution :
On the emission of one\[\alpha -\]particle from a atom, the mass number decreases four units and atomic number increases two units. On the emission of \[\beta -\]particle atomic number increases one unit but mass number remains the same. \[_{92}^{238}X\xrightarrow[{}]{-\alpha }\,_{90}^{234}Y\xrightarrow[{}]{-\beta }\,_{91}^{234}Z\] \[\because \]Number of proton in Z atom =91 \[\therefore \]Number of neutrons = mass number \[-\]number of protons \[=234-91=143\]
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