Union Government
(1) The Prime Minister shall be appointed by the President and the other Ministers shall be appointed by the President on the advice of the Prime Minister. (1A) The total number of Ministers, including the Prime Minister, shall not exceed fifteen per cent of the total number of members of the House of the People. (1B) A member disqualified under the anti-defection law (Tenth Schedule) is also disqualified from being appointed a Minister for the relevant period. (2) Ministers hold office during the pleasure of the President. (3) The Council of Ministers is collectively responsible to the House of the People. (4) Ministers take oaths of office and secrecy before the President. (5) A Minister who is not a member of either House of Parliament for six consecutive months ceases to be a Minister. (6) Salaries and allowances of Ministers are determined by Parliament by law.
The Prime Minister is appointed by the President (typically the leader who can command a majority in the Lok Sabha), and other Ministers are appointed on the Prime Minister's recommendation. The Cabinet's size is capped at 15% of the Lok Sabha's membership. Crucially, the whole Council of Ministers is collectively answerable to the Lok Sabha - meaning it must resign if it loses the confidence (a majority) of that House. A person can serve as a Minister for up to six months without being an MP, but must get elected to Parliament within that window or step down.
This collective-responsibility rule is why an entire government falls if it loses a no-confidence motion in the Lok Sabha - it's not enough for the Prime Minister alone to have support; the whole Council of Ministers stands or falls together.