$I$ carried $1000\,kg$ of watermelon in summer by train. In the beginning,the water content was $99\%$. By the time $I$ reached the destination,the water content had dropped to $98\%$. The reduction in the weight of the watermelon was $.......\,kg$.

Two radioactive materials $X_1$ and $X_2$ have decay constants $10 \lambda$ and $\lambda$ respectively. If initially they have the same number of nuclei,then the ratio of the number of nuclei of $X_1$ to that of $X_2$ will be $1 / e$ after a time:

Two solid spheres $A$ and $B$ made of the same material have radii $r_A$ and $r_B$ respectively. Both the spheres are cooled from the same temperature under the conditions valid for Newton's law of cooling. The ratio of the rate of change of temperature of $A$ and $B$ is :

For a binomial variate $X$ with $n=6$, if $P(X=2)=9 P(X=4)$, then its variance is

What are $X$ and $Y$ in the following reaction?
$CF_2Cl_2 \xrightarrow{UV} X + Y$

Which of the following statements is false regarding the properties of electromagnetic waves?