What combination of substances is specifically prohibited during transport for safety reasons?

The combination of substances specifically prohibited during transport for safety reasons is silver cyanide and battery acid. This mixture is particularly hazardous because the interaction of these two chemicals can result in the release of toxic gases or potentially cause violent reactions. Silver cyanide is a highly toxic compound, and when mixed with battery acid, which is composed primarily of sulfuric acid, the resulting reaction can produce even more dangerous compounds. The potential for lethal outcomes highlights why this combination is strictly regulated and prohibited during transport to ensure public safety and environmental protection.

The other combinations do not pose the same level of risk due to the nature of the substances involved, even though some may still be hazardous. However, silver cyanide and battery acid represent a critical safety concern that warrants explicit prohibition.