Which of the following compounds does NOT exhibit optical isomerism?

What is the value of '$$\mathrm{x}$$' in order to balance the following redox reaction by ion electron method? $$\quad \mathrm{x} \mathrm{H}_2 \mathrm{O}_2+\mathrm{ClO}_4 \rightarrow \mathrm{xO}_2+\mathrm{ClO}_2+2 \mathrm{H}_2 \mathrm{O}$$

Which among the following carbohydrates is a trisaccharide?

"Mass can neither be created nor destroyed" is the statement of