Which group elements from following are called as chalcogens?

What is the number of electrons around sulfur in $$\mathrm{H}_2 \mathrm{SO}_4$$ molecule?

An ideal gas expands by $$1.5 \mathrm{~L}$$ against a constant external pressure of $$2 \mathrm{~atm}$$ at $$298 \mathrm{~K}$$. Calculate the work done?

The rate law for the reaction $$\mathrm{A}+\mathrm{B} \rightarrow$$ product is given by rate $$=k[A][B]$$ Calculate $$[A]$$ if rate of reaction and rate constant are $$0.25 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{~s}^{-1}$$ and $$6.25 \mathrm{~mol}^{-1} \mathrm{dm}^3 \mathrm{~s}^{-1}$$ respectively $$\left[[\mathrm{B}]=0.25 \mathrm{~mol} \mathrm{dm}^{-3}\right]$$