Which of the following are meso compounds

Which of the following is a meso compound ?

Total number of compounds with Chiral carbon atoms from following is___________.   $IMAGE$

$ \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}\left(\mathrm{NO}_2\right)-\mathrm{COOH} $

$ \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CHBr}-\mathrm{CH}_2-\mathrm{CH}_3 $

$ \mathrm{CH}_3-\mathrm{CH}(\mathrm{I})-\mathrm{CH}_2-\mathrm{NO}_2 $

$ \mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}(\mathrm{OH})-\mathrm{CH}_2 \mathrm{OH} $

$ \mathrm{CH}_3-\mathrm{CH}-\mathrm{CH}(\mathrm{I})-\mathrm{C}_2 \mathrm{H}_5 $

Which of the following acids does not exhibit optical isomerism?

Which of the following pair are metamer ?

Which of the following compounds are optically active