Mark all the integers below. 2 2/3 1 -2 6.78 -25

1, -2 and -25 are integers

Explanation:
Integers are defined as whole numbers (no decimals or fractions are included).
Integers include:
set of positive numbers {1,2,3,4,etc}
zero {0}
set of negative numbers {-1,-2,-3,-4,etc}

Now, applying this to the given choices, we will find that the only three whole numbers are 1, -2 and -25. Therefore, these are the only integers.

As for other choices:
2 2/5 is a mixed number (has a fraction), therefore, not an integer
6.78 is a decimal, therefore, not an integer

Hope this helps :)