What is matter? Write its si unit
Matter is anything that has mass and volume ( i.e. occupies space). Its SI unit is mole (mol).
What do you mean by inert gases?
Atoms that are stable by following duplet or octet rule are called inert gases. For example: Helium (He), Neon (Ne), Argon (Ar), etc.
Their outermost shell is already fulfilled by maximum number of accomodable electrons. Hence, they show no reactivity towards chemical reaction. Thus, they are regarded inert.