Introduction:
The Planning Commission was a government body in India that existed from 1950 to 2014. It was responsible for formulating and implementing various development plans and policies in the country. However, one of the options listed is not a function of the Planning Commission. Let's examine each option to determine the correct answer.

Analysis:
a) Formulation of a plan: One of the primary functions of the Planning Commission was to formulate comprehensive and integrated plans for national development. These plans aimed to promote economic growth, social justice, and equity in various sectors such as agriculture, industry, infrastructure, and education.

b) Execution of development plans: This option is not a function of the Planning Commission. While the Planning Commission played a crucial role in formulating development plans, the execution and implementation of these plans were primarily the responsibility of the concerned ministries and departments of the government.

c) Appraisal of plan progress: The Planning Commission regularly monitored and appraised the progress of various development plans and programs. It assessed the achievements, shortcomings, and challenges faced in the implementation of these plans and provided feedback and recommendations for improvement.

d) Making recommendations on policy and administration: The Planning Commission played a significant role in advising the government on various policy matters related to economic and social development. It made recommendations on policy formulation, resource allocation, and administrative reforms to ensure effective implementation of development plans.

Conclusion:
Based on the analysis, it can be concluded that option 'b' (Execution of development plans) is not a function of the Planning Commission. The Planning Commission primarily focused on the formulation of plans, appraisal of plan progress, and making recommendations on policy and administration. The execution and implementation of development plans were the responsibility of the concerned ministries and departments of the government.