South is playing a 3NT contract. What card should West lead holding
The correct lead is the Q of spades. The lead of a Q against a NT contract is a standard lead requesting (ordering!) East to play the J if holding that card. The reason?
East needs to “get out of the way.” If East does not play the spade J, West will place that card in the South hand and will switch suits, because to lead another spade will make both the A and J good in the South hand. If East plays the J, West will eventually win 4 spade tricks and the A of diamonds to set the contract.
West is on lead against a 3NT contract holding. Which spade does West lead?
The A of spades. Against a NT contract, the lead of an ace asks (orders!) partner to play his highest honor in that suit unless such a play will obviously give up a trick. Note that if East holds K5 of spades and does not drop the K under the ace, the suit will block and West will take 1 spade trick and East will take 1 spade trick. Playing the K allows West to take the first 6 tricks.