The correct answer is option 1, once. This means that the term of the Lok Sabha has been extended up to 6 years only once. The Lok Sabha is the lower house of the Indian Parliament and its regular term is for 5 years. However, there have been occasions where the term has been extended beyond 5 years due to various reasons such as national emergency or war. In such cases, the term can be extended by passing a resolution in the Lok Sabha. However, it is important to note that these extensions are temporary and the regular term of the Lok Sabha is still 5 years. It is also worth mentioning that this extension up to 6 years happened only once, as per the provided information.