This week, Japan is hosting the G7 leaders in Hiroshima in an effort to highlight the risks of nuclear weapons and advance the cause of disarmament. However, with China expanding its arsenal and North Korea and Russia making nuclear threats, there may not be much desire for aggressive action to achieve Prime Minister Fumio Kishida’s stated objective of a “world free of nuclear weapons.” Following are some queries and responses regarding nuclear weapons and Japan’s objectives: Which G7 states are nuclear-armed? Three G7 members — the United States, Britain and France — have nuclear arsenals, with Washington holding an estimated...