Question

mention the communities termed as desirable and undesirable by Nazis

Answer 1

Desirable-pure blooded Aryans.

Undesirable- jews,gypsies,mentally and physically ill germans and all other non-germans.

Answer 2

National Socialism (German: Nationalsozialismus), more commonly known as Nazism  is the ideology and set of practices associated with the 20th-century German Nazi Party, Nazi Germany and other far-right groups. Usually characterized as a form of fascism that incorporates scientific racism and antisemitism, Nazism's development was influenced by German nationalism(especially Pan-Germanism), the Völkisch movement and the anti-communist Freikorps paramilitary groups that emerged during the Weimar Republic after Germany's defeat in First World War.
Nazism subscribed to theories of racial hierarchy and Social Darwinism, identifying the Germans as a part of what the Nazis regarded as an Aryan or Nordic master race. It aimed to overcome social divisions and create a German homogeneous society based on racial purity which represented a people's community (Volksgemeinschaft). The Nazis aimed to unite all Germans living in historically German territory, as well as gain additional lands for German expansion under the doctrine of Lebensraum and exclude those who they deemed either community aliens or "inferior" races. The term "National Socialism" arose out of attempts to create a nationalist redefinition of "socialism", as an alternative to both international socialism and free market capitalism. Nazism rejected the Marxist concept of class conflict, opposed cosmopolitan internationalism and sought to convince all parts of the new German society to subordinate their personal interests to the "common good" and accept political interests as the main priority of economic organization.