A mid-term poll is conducted when the Lok Sabha is dissolved before completion of its term. This means that option 1 is the correct answer.

Option 2, when an elected member resigns from his seat, does not necessarily lead to a mid-term poll. In such cases, a by-election is conducted to fill the vacant seat, but it does not require the dissolution of the entire Lok Sabha.

Option 3, when there are discrepancies in voting, also does not necessarily lead to a mid-term poll. Voting discrepancies can be addressed through legal procedures and do not automatically result in the dissolution of the Lok Sabha.

Option 4, when all MPs of a political party resign, also does not lead to a mid-term poll. Resignation of MPs can lead to a loss of majority for a ruling party, but it does not require the dissolution of the entire Lok Sabha.