Answer: 0.294 mol of 
present in the reaction vessel.
Explanation:
Initial moles of 
= 0.682 mole
Initial moles of = 0.440 mole
Volume of container = 2.00 L
Initial concentration of 
Initial concentration of 
equilibrium concentration of 
The given balanced equilibrium reaction is,
Initial conc. 0.341 M 0.220 M 0 M
At eqm. conc. (0.341-x) M (0.220-x) M (2x) M
The expression for equilibrium constant for this reaction will be,
![K_c=\frac{[HBr]^2}{[Br_2]\times [H_2]}](https://tex.z-dn.net/?f=K_c%3D%5Cfrac%7B%5BHBr%5D%5E2%7D%7B%5BBr_2%5D%5Ctimes%20%5BH_2%5D%7D)
we are given : (0.341-x) = 0.268 M
x= 0.073 M
Thus equilibrium concentration of = (0.220-x) M = (0.220-0.073) M = 0.147 M
![[Br_2]=\frac{moles}{volume}\\0.147=\frac{xmole}{2.00L}\\\\x=0.294 mole](https://tex.z-dn.net/?f=%5BBr_2%5D%3D%5Cfrac%7Bmoles%7D%7Bvolume%7D%5C%5C0.147%3D%5Cfrac%7Bxmole%7D%7B2.00L%7D%5C%5C%5C%5Cx%3D0.294%20mole)
Thus there are 0.294 mol of present in the reaction vessel.
Because I can't see your options, all I can say is to look for the one whose numbers can't be simplified any further
The number of significant figures within a number are the amount digits that are required to specify a number to a certain degree of accuracy. In the number, 0.0645 g, the 6 is the most significant figure and 4 is the second most significant figure. Therefore, rounding to two significant figures yields 0.064g.
PV=nRT
So
NRT/P=V ...
SI units for pressure is pascals so 81.8KPA = 81.8 x 10^3 PA
SI units for temperature is kelvin so 15 degrees celsius = 15 +273 = 288K
(0.582 x 8.314 x 288)/81.8 x 10^3 = 0.017 m3 (cubic meters)
