nackt
naked
Without any clothing on the body; unclothed.
Nach dem Saunagang springen viele nackt in den kalten See.
After going to the sauna, many people jump naked into the cold lake.

naked
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naked
Without any clothing on the body; unclothed.
Nach dem Saunagang springen viele nackt in den kalten See.
After going to the sauna, many people jump naked into the cold lake.

'Nackt' (naked) can describe not only what something is like (adjective), but also how an action is carried out (adverb). In this case, it is not declined and usually comes after the verb.
Im Sommer schlafen viele Menschen nackt, weil es so heiß ist.
In summer, many people sleep naked because it is so hot.
To express that someone is completely naked, the intensifier 'splitterfasernackt' (stark naked) is often used colloquially.
Nach dem Schlammbad standen die Kinder splitterfasernackt unter der Dusche.
After the mud bath, the children stood stark naked under the shower.
In the figurative meaning, 'nackt' (bare / naked) is often used in fixed expressions to mean 'unvarnished' or 'undistorted.' Typical phrases are 'die nackte Wahrheit' (the naked truth), 'die nackten Tatsachen' (the bare facts), or 'die nackten Zahlen' (the bare numbers).
Der Bericht zeigte die nackten Fakten der finanziellen Situation.
The report showed the bare facts of the financial situation.
In biology, 'nackt' (naked / bare) is often used as the first part of compound nouns to refer to animals or plants without a typical covering. A well-known example is 'die Nacktschnecke' (slug, literally: naked snail).
Der Nacktmull ist ein Säugetier, das fast keine Haare hat.
The naked mole-rat is a mammal that has almost no hair.
pure / in
'rein' and 'nackt' can both mean that something is shown without additions or decoration. 'rein' fits better when something is unmixed or pure, for example a substance or an idea. 'nackt' has a stronger sense of 'without a covering' or 'without everything that normally comes with it'. It is often used figuratively, for example in 'nackte Zahlen' (bare figures). The words can be confused because both can refer to something basic. A practical guide: 'rein' emphasizes purity or being unmixed, while 'nackt' emphasizes being uncovered or unadorned.

Im Bericht stehen nur die nackten Zahlen, aber keine Erklärung dazu.
The report contains only the bare figures, but no explanation for them.
Für den Tee nimmt meine Kollegin reines Wasser ohne Zusätze.
For the tea, my colleague uses pure water without additives.