(1) It isn't hard to look this up.

"Hydrogen cyanide is a gas.

Sodium and potassium cyanide are salts, which are solid.

Zyklon B is a diatomaceous earth permeated with hydrogen cyanide.

*The poisonous part of cyanide is the cyanide anion.

*What the anion is attached to isn’t that important is toxicity.

The attachment affects how it is dispersed.

Potassium cyanide and sodium cyanide are both salts.

They are solids at room temperature. However, they can be dissolved in water.

Solutions of these salts are highly toxic.

You can kill animals by pouring the solution on them. However, they don’t spread as gases.

The salts can’t evaporate from the solution.

The cyanide anion with hydrogen can form a gas, hydrogen cyanide.

The gas can spread. It is still toxic.

The way to get hydrogen cyanide from either salt is add powerful acid to the salt solution.

For example, here is the reaction with sulfuric acid.

H2SO4+2KCN→K2SO4+2HCN"

https://www.quora.com/Whats-the-difference-between-potassium-cyanide-sodium-cyanide-and-hydrogen-cyanide?share=1

Cyanide

A cyanide is a chemical compound that contains the group C≡N.

This group, known as the cyano group,

consists of a carbon atom triple-bonded to a nitrogen atom.

In inorganic cyanides, the cyanide group is present as the anion CN⁻.

Soluble salts such as sodium cyanide and potassium cyanide are highly toxic.

Hydrocyanic acid, also known as hydrogen cyanide, or HCN,

is a highly volatile liquid that is produced on a large scale industrially.

It is obtained by acidification of cyanide salts.

Wikipedia

(2) Zyklon B was cheap and able to be smuggled past Red Cross and other inspections because it was designed and packaged specifically for relieving prisoner suffering and illness, as an anti parasitic.