The correct answer is option 1: 1 and 2 only.

This means that the introduction of polymer/plastic Rs. 10 notes on a field trial basis is aimed at achieving two objectives: increasing the lifetime of the notes and combating counterfeiting.

1. Increasing the lifetime of the notes: Polymer/plastic notes have a longer lifespan compared to paper notes. They are more durable and resistant to wear and tear, resulting in a reduction in the frequency of replacement. This objective helps in saving costs associated with printing and circulation of currency.

2. Combating counterfeiting: Polymer/plastic notes are more difficult to counterfeit compared to paper notes. They often have advanced security features such as holograms, windowed security threads, and microprinting, which make it easier to identify genuine notes. By introducing polymer/plastic notes, the government aims to reduce the prevalence of counterfeit currency in circulation.

It is important to note that the cost of minting currency (mentioned in option 3) is not one of the objectives mentioned in the question, and hence option 3 is not correct.