Though he has lot of money, yet all his plans are built upon sand.

The idiom "built upon sand" refers to something that is based on a weak or unreliable foundation.

Imagine building a house on loose sand instead of solid ground. The house would be unstable and might collapse easily. Similarly, plans that lack a strong and reliable foundation are likely to fail.

In the given sentence, the person has a lot of money, but all his plans are "built upon sand", meaning that his plans are not based on a strong or secure foundation.

Option A: Established on insecure foundations is correct because it conveys the exact meaning of the idiom. An insecure foundation is weak or unreliable, just like loose sand.

Example: His business plans were built upon sand because he had not done proper research.

Remember: Built upon sand = Established on insecure foundations.