What is the hydrostatic test date of a cylinder marked with the numbers 12343 PST 6 96?

The hydrostatic test date of a cylinder is indicated by the numbers following the "PST." In this case, "6 96" represents the month and year the test was conducted. Specifically, the "6" refers to June, while "96" denotes the year 1996. Therefore, the correct interpretation of this marking is that the cylinder was hydrostatically tested in June 1996.

The other options do not accurately reflect the marking on the cylinder. For example, June 1965 does not align with the numbers present on the tank, and January or December 1996 are also inconsistent with the "6 96" marking, which specifically indicates June of that year. Thus, the correct answer is June 1996, as indicated by the "6 96" date format.