In the transformation of $_{92}^{238} \mathrm{U}$ to $_{92}^{234} \mathrm{U}$, if one emission is an $\alpha$-particle, what should be the other emission(s)?

(B) Two $\beta^{-}$ and one $\beta^{+}$

(C) One $\beta^{-}$ and one $\gamma$

(D) One $\beta^{+}$ and one $\beta^{-}$

JEE Main · 2006 · 30 Apr 2006 · Offline · Chemical Kinetics

In the transformation of

_{92}^{238} U

_{92}^{234} U

, if one emission is an

α

-particle, what should be the other emission(s)?

Answer: (A)

Going from

_{92}^{238} U

_{92}^{234} U

, the mass number falls by four while the atomic number is unchanged. A single

α

-emission removes a

_{2}^{4} He

nucleus, lowering the mass by four and the atomic number by two to give

_{90}^{234} Th

. The atomic number must now climb back from 90 to 92, and since each

β^{-}

emission raises it by one while leaving the mass untouched, two

β^{-}

particles are required. The accompanying emissions are therefore two

β^{-}

particles.

JEE Main · 2006 · 30 Apr 2006 · Offline · Single correct option