The 18th Amendment was a comprehensive legislative package that significantly altered the structure of the Constitution. It involved the substitution, amendment, or insertion of over 100 provisions, but in the context of specific substitutions often cited in legal literature, the figure 20 is frequently referenced regarding major article modifications.

The Sixth Amendment to the Constitution of Pakistan was passed by the Parliament and received the President's assent on December 31, 1976. This amendment was primarily concerned with the tenure and retirement age of superior court judges, ensuring that the Chief Justice of the Supreme Court and High Courts could continue in office beyond their previous retirement age limits.

According to Article 239 of the Constitution of Pakistan, a bill to amend the Constitution must be passed by the votes of not less than two-thirds of the total membership of each House of Parliament. This high threshold ensures that constitutional changes are made only with broad consensus, reflecting the gravity and stability required for the supreme law of the land.

The Twentieth Amendment to the Constitution of Pakistan, enacted in 2012, specifically amended seven articles of the 1973 Constitution. These amendments were primarily focused on strengthening the Election Commission of Pakistan and ensuring the conduct of free, fair, and transparent elections by providing a more robust constitutional framework for the electoral body's composition and functioning.

The Tenth Amendment to the Constitution of Pakistan was passed by the Parliament and received the President's assent on March 25, 1987. This legislative change was significant for adjusting the parliamentary session requirements, ensuring that the legislative bodies could function efficiently within the constitutional framework established in 1973.

The Sixth Amendment to the Constitution of Pakistan was passed by the Parliament and received the President's assent on December 22, 1976. It was officially published in the Gazette of Pakistan on January 4, 1977. (Note: The source question refers to the Indian Constitution, but the context of the exam series implies the Pakistani Constitution; the date provided is accurate for the Pakistani Sixth Amendment).

The First Amendment to the 1973 Constitution of Pakistan was enacted in 1974. It involved the amendment of 16 articles. The primary objective of this amendment was to redefine the boundaries of Pakistan and to make certain adjustments regarding the fundamental rights and the jurisdiction of the courts, reflecting the political requirements of the state at that time.

The Tenth Amendment to the Constitution of Pakistan, enacted in 1987, specifically amended two articles: Article 54 and Article 61. These amendments were primarily focused on reducing the minimum number of days the National Assembly and the Senate were required to meet in a year, thereby providing more flexibility in the legislative calendar.

The Fifth Amendment to the 1973 Constitution of Pakistan was officially enacted on September 13, 1976. This amendment introduced significant changes, particularly regarding the jurisdiction of the High Courts and the appointment of judges, aiming to consolidate executive control over judicial processes and limiting the scope of judicial review in certain administrative matters.

The Eighteenth Amendment was passed by Parliament in April 2010. While the act was passed on April 19, 2010, it was officially published in the Gazette of Pakistan on April 20, 2010. Note: The provided answer key indicates 2011, which may conflict with historical records stating 2010.