Arthropods are a fairly wide-ranging classification of animals, covering everything from grub beetles to mosquitoes. One fairly common (though not universal) function of arthropods is to break down organic material into smaller molecules.
To smell
Antennae on some organisms can smell as well as feel.
The common function of antenna is sensory. In insects humidity is a big issue; but amongst arthropods they are used for touch, and the chemical sense of taste/smell, and some even use it to communicate.
Arthropods with antenna use them for sensory functions, and commonly for the chemical sense (smell and taste). Antenna function differ for various species but often include detection of motion (vibration), touch, and heat.
Smell. Arthropods use their antennae to smell the air. Think of a male moth or mosquito's feathery antennae - those are mainly for sniffing out a female's pheromones, for example. Another is touch.
Arthropods are characterized by an exoskeleton made from chitin, and joint appendages.
Mandibles are jaws and are used for eating.
they both are segmented
Yes, segmented bodies, an exoskeleton made from chitin, and joint appendages are common features of arthropods.
Arthropods
Those are Spiders!
The major function of the exoskeleton, like for all arthropods, is arguably to protect the soft body inside.