1)
What is the meaning of "Gas Yisov"?
1.
Radak: [It will be turned] to Gas. There are many [verses] like this [in which the prefix Lamed is omitted].
2)
Why did they send it to Gas?
1.
Malbim: The officers attributed [their afflictions] to chance. They wanted to test if it will afflict people there. They did not send it to z city near Ashdod, rather, to Gas far away, for they thought that it is a contagious disease. It would not spread to a far place.