Teacher: Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.
Teacher: Now, understand the problem? If you are still confused, see the following example:
Sentence1: pesticides cause pollution. 
Sentence2: pollution can harm animals.
Solution: pollution.
Reason: The word "pollution" is common to Sentence1 and Sentence2. So, it's a good answer.

Now, solve this instance: Sentence1: if a neutral atom loses an electron then an atom with a negative charge will be formed. 
Sentence2: if an atom loses an electron then it forms an ion.
Student:
electron