If the temperature of metal sphere increases by $\;\bigtriangleup t\;$ , the fractional change in its moment of inertia is $\;(\alpha \;= Coefficient\; of\; linear \;expansion )$

Question

$(a)\;2 \alpha \bigtriangleup t\qquad(b)\;\alpha \bigtriangleup t\qquad(c)\;2 \alpha\qquad(d)\;2 \bigtriangleup t$