Were chemical/biological weapons used in combat during World War 2?

Depends. There was a lot of arms race in tank armor and anti-tank weapons during WWII. In 1939 anti-tank rifles were enough to penetrate armors of almost all armored vehicles in the field - including side armors of battle tanks. By 1943 they were almost useless.

I remember reading somewhere, that British BOYS anti-tank rifle used in North Africa was step-by-step degraded from primary anti-tank weapon into support weapon against unarmored/lightly armored vehicles, then against machine-gun emplacements, and then eventually to hunt crocodiles in lakes and rivers near military bases…

BBC History Magazine this month has an article about a mustard gas factory somewhere in the valleys of North Wales (there’s nothing about it on the website though, so I can’t cite anything). It says that they were making large quantities of it in the (apparently mistaken) belief that the Nazis had large quantities in reserve. Interestingly, it seems that they believed the same thing about the British.
After the war, as I recall, the reserves were dumped in a trench somewhere in the Irish Sea.

No more swimming in the Irish Sea for me.

Actually to be GQ the German’s did use mustard gas in Poland during the war, they just maintained it was a mistake and the Poles (probably retaliated). This is the best documented case but they may (or may not have used it in the elsewhere in the east)

1939, Polish troops used chemical training mines containing diluted mustard agent to mine a bridge near Jaslo, injuring 14 German soldiers. It is unclear whether this was a mistake or an attempt at retaliation for the reported use of chemical bombs by the Germans in Warsaw (on September 3, 1939, a number of sulfur mustard-containing bombs were dropped on a Warsaw suburb - the Germans aknowledged this in 1942, indicating it was accidental). The Germans may also have used mustard gas-containing munitions on a few occasions in the Crimea and elsewhere in Poland, but these appear to have either been genuine mistakes or instances of low-level commanders acting without authority.