Can we claim exempt income u/s 10 in the itr2 - which is not shown in form 16.

Will you please clarify, under which sub-section of section 10 of IT act, the income is exempt?

Section10(14) - Office Help Assistance - who is engaged for the help of official duties... 

Section 10(14) (i) any such special allowance or benefit, not being in the nature of a perquisite within the meaning of clause (2) of section 17, specifically granted to meet expenses wholly, necessarily and exclusively incurred in the performance of the duties of an office or employment of profit, as may be prescribed, to the extent to which such expenses are actually incurred for that purpose ..

For that exemption you have to submit the bills of your expenditure to your accounts.

Without the actual expenditure bills/proofs, it is taxable.

Most probably it comes under  10(14)(i)  s.no 4  - helper allowance

"Any allowance by whatever name called granted to meet the expenditure incurred  on a helper where such helper is engaged for  performance  of duties of an office or employment of profit"

Amount received or amount actually spent for the performance of duty  which ever is less.