CHARACTERISTICS
Venus is similar to the Earth in size and mass and therefore in density. Its similar density suggests similar composition. The radius of Venus is 6052 km versus the terrestrial 6371 km, 95% of the Earth's radius.
The volume of Venus is 86% of that of the Earth and its mass 80% of the terrestrial mass. While this may reflect similar internal composition.
Similarities are not reflected in the atmosphere which is 96.5% CO2 and 3.5% N2 compared with the 78% N2 and 21% O2 composition of the atmosphere of the Earth.
However, this difference may have much to do with the lack of water on Venus.