If rubberbands are solid then how can they stretch ?
Rubber stretches because its long chains can straighten out.
Rubber is a natural polymer.
It contains long chains that are cross-linked to each other (at the red spots in the image below.
If you stretch the rubber, the chains do not slip past each other, but they do tend to straighten out.
After the force is removed, the cross-links cause the rubber to resume its original size and shape.
solids can be elastic too
most elastic materials are polymers with lots of crosslinking chemical bonds. When the material is stretched or compressed or twisted, the chemical bonds 'relax; and allow the object to change shape. As long as the force applied isn't too much, the object can return to its original dimensions.
This is defined and quantified by material properties such as Young's Modulus and Poisson's ratio.