Answer:
<em>The sequence is geometric.</em>
Step-by-step explanation:
In Arithmetic sequence, there is a common difference between any two consecutive terms but in Geometric sequence, there is a common ratio between any two consecutive terms.
Given sequence is: 50, -50, 50, -50,.................
Lets assume, the terms as 
<em><u>Checking for common difference:</u></em>

As there is no common difference, so it's not an arithmetic sequence.
<u><em>Checking for common ratio</em></u>

As there is a common ratio, so it's a geometric sequence.