Question

Transformation of uranium-238 into thorium-234 is done by the process :

• A. gamma decay
• B. nuclear fusion
• C. alpha decay
• D. positron emission
• E. nuclear fission

Answer 1

The correct option is C alpha decay

$U\left(238\right)\to Th\left(234\right)+He\left(4\right)$
As the mass number of uranium is 238 whereas that of the thorium is 234, hence, 238 - 234 = 4, it means there is decreasse in 4 mass number, so definitely there was Alpha decay.
Alpha particle is He neucleus.