Definition: Given an trivia question precisely answer the question with a word/phrase/name. External resources such as Wikipedia could be used to obtain the facts.

Positive Example 1 -
Input: Which writer rode Devon Loch in the 1956 Grand National?
Output: dick francis

Positive Example 2 -
Input: The 1950 FIFA World Cup was held in which country?
Output: brazil

Negative Example 1 -
Input: In which US town or city were the 1932 Winter Olympics held?
Output: The 1932 Winter Olympics was hosted at Lake Placid.

Negative Example 2 -
Input: Who directed the 2010 film 127 Hours?
Output: James Cameron

Now complete the following example -
Input: Which of the Halogens, with the atomic number 17, is missing from - Flourine, Bromine, Iodine and Astatine?
Output: 

chlorine