Question

${}_{98}{Cf}^{246}$ was formed along with a neutron when an unknown radioactive substance was bombarded with ${}_6{C}^{12}$. The unknown substance was :

• A. ${}_{91}{Pa}^{234}$
• B. ${}_{90}{Th}^{234}$
• C. ${}_{92}{U}^{235}$
• D. ${}_{92}{U}^{238}$

Answer 1

The correct option is C ${}_{92}{U}^{235}$

Let the unknown radioactive substance be ${}_x{A}^y$.
${}_x{A}^y{+}_6{C}^{12}{⟶}_{98}{Cf}^{246}{+}_0{n}^1$
On comparing atomic numbers, we get
$x+6=98+0$
$x=98-6=92$
On comparing mass numbers, we get
$y+12=246+1$
$y=247-12$
$=235$
Since, uranium has the atomic number 92, thus, the given unknown substance was ${}_{92}{U}^{235}$.