What is the correct order of the planets in the solar system

That completely depends on what characteristic you use to sort them.

You could list the planets in order of their mass, diameter, density,

rotation period, surface temperature, orbital eccentricity, inclination

to the ecliptic, surface reflectivity, etc. Each sorting criterion would

give you a different list.

In the order of the length of the semi-major-axis of each planet's orbit,

the sequence, from smallest to largest, is ...

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

the former planet Pluto.

There are 8 planets in the solar system and the correct order is:

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.