Question

Why is $HF$ acid stored in plastic bottles?

Answer 1

Hint: Hydrogen fluoride is highly soluble and with excessive intake leads to dental and skeleton degradation and is indirectly responsible for the most lethal gas-related zolcaric event.

Complete step by step answer:
Plastic Chemical storage:- Storing in the right container is the first way to ensure safety when handling strong acid and bases. A material that is likely to react with the chemical it helds, like a metal container, or break easily when dropped, like a glass container, isn’t going to be suitable for a substance like nitric acid, for example.
This is why there are a variety of plastic materials used for storing acid and bases, so that each container can accommodate the unique properties of individual chemicals. For example the plastic polypropylene can be used to store corrosive chemicals.
Hydrofluoric acid $\left( {HF} \right)$ is a solution of hydrogen fluoride in water-hydrofluoric acid is a highly corrosive acid, capable of dissolving many materials, especially oxides.
Because of its high reactivity toward glass and moderate reactivity toward many metals, hydrofluoric acid is usually stored in plastic containers ( although polytetrafluoroethylene is slightly permeable to it )

Hydrofluoric acid attacks the silicon oxide in most types of glass. It also dissolves many metals ( not nickel or its alloys, gold, platinum or silver ) and most plastics fluorocarbons such as Teflon $TFE$ & $FEP$ chlorosulfonated polyethylene, natural rubber and neoprene all are resistant to hydrofluoric acid. Hydrofluoric acid is so corrosive because the fluoride ion is highly reactive. Even so, it is not considered a ‘strong’ acid because it also does not completely dissociate in water.
Hydrofluoric acid is classified as a weak acid because of its lower dissociation constant compared to the strong acids. It ionizes in aqueous solution in a similar fashion to other common acids:

$HF + {H_2}O \rightleftharpoons {H_3}{O^ + } + {F^ - }$
It is the only hydrohalic acid that is not considered a strong acid, i.e. it is not fully ionized in dilute aqueous solutions.
When the concentration of $HF$ approaches $100\% $ , the acidity increases dramatically because of the following equilibrium.
$2HF \rightleftharpoons {H^ + } + FH{F^ - }$
The bifluoride $FH{F^ - }$ anion is stabilized by the very strong hydrogen-fluorine hydrogen bond.
Hydrogen fluoride gas is an acute poison that may immediately and permanently damage lungs and the corneas of the eyes. Aqueous hydrofluoric acid is a contact poison with the potential for deep, initially painless burns and ensuing tissue death. By interfering with body calcium metabolism, the Concentrated acid may also cause systemic toxicity and erentual cardiac arrest and fatality, after contact with as little as $160{\text{ c}}{{\text{m}}^2}$( $25$ square inches ) of skin.

Note:
Hydrofluoric acid must be stored in a tightly closed container made from either polyethylene, fluorocarbon, or lead. Also, in a cool dry place away from other chemicals or materials.