  We present a comprehensive investigation of HI (super)clouds, molecular
clouds (MCs), and star formation in the Carina spiral arm of the outer Galaxy.
Utilizing HI4PI and CfA CO survey data, we identify HI clouds and MCs based on
the ($l$, ${v_\mathrm{LSR}}$) locations of the Carina arm. We analyzed 26 HI
clouds and 48 MCs. Most of the identified HI clouds are superclouds, with
masses exceeding $10^6~{\mathrm{M_\odot}}$. We find that 15 of these
superclouds have associated MC(s) with ${M_\mathrm{HI}} \gtrsim
10^6~{\mathrm{M_\odot}}$ and ${\Sigma_\mathrm{HI+H_2}} \gtrsim$ 50
${\mathrm{M_\odot}} \rm pc^{-2}$. Our virial equilibrium analysis suggests that
these CO-bright HI clouds are gravitationally bound or marginally bound. We
report an anti-correlation between molecular mass fractions and Galactocentric
distances, and a correlation with total gas surface densities. Nine CO-bright
HI superclouds are associated with HII regions, indicating ongoing star
formation. We confirm the regular spacing of HI superclouds along the spiral
arm, which is likely due to some underlying physical process, such as
gravitational instabilities. We observe a strong spatial correlation between
HII regions and MCs, with some offsets between MCs and local HI column density
peaks. Our study reveals that in the context of HI superclouds, the star
formation rate surface density is independent of HI and total gas surface
densities but positively correlates with molecular gas surface density. This
finding is consistent with both extragalactic studies of the resolved
Kennicutt-Schmidt relation and local giant molecular clouds study of Lada et
al. (2013), emphasizing the crucial role of molecular gas in regulating star
formation processes.
