ANSWER: Historical trivia: What was the reason given by the Nazis for Kreystalnacht?

OK, I should accept "(4) all of the above" since to some extent they were all true.

But, the assassination of Ernst vom Rath, a official at the German Embassy in Paris, by Herschel Grynszpan on 7 November 1938 was the event which most closely caused Krystalnacht.  The German government retaliated to this event by barring Jewish children from German state elementary schools, indefinitely suspending Jewish cultural activities, and putting a halt to the publication of Jewish newspapers and magazines, including the three national German Jewish newspapers

There is ironic twists to this event:  Vom Rath was a professional diplomat with the Foreign Office who expressed anti-Nazi sympathies, largely based on the Nazis' treatment of the Jews, and was under Gestapo investigation for being politically unreliable at the time he was killed.

But, an act of violence created far more violence.  In fact, looking at Krystalnacht points out the truth of  N. A. Browne's The Myth of Nazi Gun Control:

The Third Reich did not need gun control (in 1938 or at any time thereafter) to maintain their power. The success of Nazi programs (restoring the economy, dispelling socio-political chaos) and the misappropriation of justice by the apparatus of terror (the Gestapo) assured the compliance of the German people. Arguing otherwise assumes a resistance to Nazi rule that did not exist. Further, supposing the existance of an armed resistance also requires the acceptance that the German people would have rallied to the rebellion. This argument requires a total suspension of disbelief given everything we know about 1930s Germany. Why then did the Nazis introduce this program? As with most of their actions (including the formation of the Third Reich itself), they desired to effect a facade of legalism around the exercise of naked power. It is unreasonable to treat this as a normal part of lawful governance, as the rule of law had been entirely demolished in the Third Reich. Any direct quotations, of which there are several, that pronounce some beneficence to the Weapons Law should be considered in the same manner as all other Nazi pronouncements - absolute lies. (See Bogus Gun Control Quotes and endnote [1].)

A more farfetched question is the hypothetical proposition of armed Jewish resistance. First, they were not commonly armed even prior to the 1928 Law. Second, Jews had seen pogroms before and had survived them, though not without suffering. They would expect that this one would, as had the past ones, eventually subside and permit a return to normalcy. Many considered themselves "patriotic Germans" for their service in the first World War. These simply were not people prepared to stage violent resistance. Nor were they alone in this mode of appeasement. The defiance of "never again" is not so much a warning to potential oppressors as it is a challenge to Jews to reject the passive response to pogrom. Third, it hardly seems conceivable that armed resistance by Jews (or any other target group) would have led to any weakening of Nazi rule, let alone a full scale popular rebellion; on the contrary, it seems more likely it would have strengthened the support the Nazis already had. Their foul lies about Jewish perfidy would have been given a grain of substance. To project backward and speculate thus is to fail to learn the lesson history has so painfully provided.

The simple conclusion is that there are no lessons about the efficacy of gun control to be learned from the Germany of the first half of this century. It is all too easy to forget the seductive allure that fascism presented to all the West, bogged down in economic and social morass. What must be remembered is that the Nazis were master manipulators of popular emotion and sentiment, and were disdainful of people thinking for themselves. There is the danger to which we should pay great heed. Not fanciful stories about Nazi's seizing guns.

I would also add that you read this paper for further debunking of the Hitler non-sense.

But, the bottom line is that no one who knows anything about the Second World War and the Third Reich buys into the "Hitler was for gun control."

If anything, Hitler was pro-gun.  He probably would have welcomed armed Jewish resistance as a reason to exterminate the Jews. 

Remember that the usual result of Jewish Ghetto uprisings was a quicker trip to one of the dedicated Operation Reinhard extermination camps (e.g., The survivors of the Warsaw Ghetto were sent to Treblinka).

FYI, the first nation to have an actual gun registration programme was Great Britain (The Gun Licence Act 1870, Pistol Act of 1903, and The Firearms Act of 1920)--Where is the British Genocide?  I would also add that the Home Secretary ruled that self-defence was no longer a suitable reason for applying for a firearm certificate in 1937, and directed police to refuse such applications on the grounds that "firearms cannot be regarded as a suitable means of protection and may be a source of danger"