With the 'quantitydropped' attribute you can set the quantity of dropped items/blocks.
Valid values are integers between 0 and 64 (including both) and a range like '1-4' which means the block drops between 1 and 4 items/blocks.
Default value: 1
Damage value default value: 1
quantitydropped="1";
quantitydropped="1-5";