Gymnosperms lack true fruits because.....

Which one of the following is not an iso-electronic pair?

Half-life of a radioactive substance is $20 \, min$. The difference between the points of time when it is $33 \%$ disintegrated and $67 \%$ disintegrated is approximately .......... $min$.

Name the gas that can readily decolourise acidified $KMnO_4$ solution.

Two spherical bodies of mass $M$ and $5M$ and radii $R$ and $2R$ respectively are released in free space with an initial separation between their centres equal to $12\,R$. If they attract each other due to gravitational force only,then the distance covered by the smaller body just before collision is (in $, R$)

Which one of the following statements about packing in solids is incorrect?