Short answers, pulled from the story.
Russia possesses 5,459 nuclear warheads, the largest arsenal in the world, with 1,718 already deployed. Russia and the United States together hold 88% of all nuclear weapons in existence, and Russia's stockpile is growing while the United States' is shrinking.
The Tsar Bomba was a Soviet nuclear device detonated over the Arctic island of Novaya Zemlya in 1961. It yielded 50 megatons, making it by far the largest nuclear explosion in history. The Soviet Union carried out 715 nuclear tests in total, from its first test in 1949 until 1990.
On the 2nd of April 1979, anthrax spores were accidentally released from a Soviet military facility in Sverdlovsk, 1,500 km east of Moscow, infecting 94 people and killing most of them over six weeks. The incident revealed to the Western Bloc that the Soviet Union was secretly operating a biological weapons program in violation of the Biological Weapons Convention it had ratified in 1975.
In his the 1st of March 2018 state-of-the-nation address, Putin announced the RS-28 Sarmat ICBM, the Avangard hypersonic glide vehicle, the Burevestnik nuclear-powered cruise missile, and a nuclear-powered underwater torpedo. Putin described the Avangard as capable of traveling at 20 times the speed of sound and called it "absolutely invulnerable for any missile defense system."
In March 2018, former GRU agent Sergei Skripal and his daughter Yulia were poisoned with Novichok in Salisbury, United Kingdom. In August 2020, Russian opposition figure Alexei Navalny was poisoned with Novichok in Tomsk, Russia. A joint investigation by Bellingcat, CNN, Der Spiegel, The Insider, and El Pais implicated Russia's Federal Security Service in the Navalny poisoning.
Russia deployed Iskander-M nuclear-capable missile systems to Belarus in 2023, with Putin announcing the first warhead delivery on the 16th of June 2023 at the St. Petersburg International Forum. The warheads are believed to carry variable yields between 5 and 50 kilotons. On the 10th of December 2024, Belarusian President Lukashenko stated that Belarus was hosting "dozens" of Russian warheads.