  The newly operational JWST offers the potential to study the atmospheres of
distant worlds with precision that has not been achieved before. One of the
first exoplanets observed by JWST in the summer of 2022 was WASP-96 b, a
hot-Saturn orbiting a G8 star. As part of the Early Release Observations
program, one transit of WASP-96 b was observed with NIRISS/SOSS to capture its
transmission spectrum from 0.6-2.85 microns. In this work, we utilise four
retrieval frameworks to report precise and robust measurements of WASP-96 b's
atmospheric composition. We constrain the logarithmic volume mixing ratios of
multiple chemical species in its atmosphere, including: H$_2$O = $-3.59 ^{+
0.35 }_{- 0.35 }$, CO$_2$ = $-4.38 ^{+ 0.47 }_{- 0.57 }$ and K = $-8.04 ^{+
1.22 }_{- 1.71 }$. Notably, our results offer a first abundance constraint on
potassium in WASP-96 b's atmosphere, and important inferences on carbon-bearing
species such as CO$_2$ and CO. Our short wavelength NIRISS/SOSS data are best
explained by the presence of an enhanced Rayleigh scattering slope, despite
previous inferences of a clear atmosphere - although we find no evidence for a
grey cloud deck. Finally, we explore the data resolution required to
appropriately interpret observations using NIRISS/SOSS. We find that our
inferences are robust against different binning schemes. That is, from low $R =
125$ to the native resolution of the instrument, the bulk atmospheric
properties of the planet are consistent. Our systematic analysis of these
exquisite observations demonstrates the power of NIRISS/SOSS to detect and
constrain multiple molecular and atomic species in the atmospheres of hot giant
planets.
