An element having configuration 1s2 2s2 2p6 3s2 3p6 4s1 will form basic oxide.
As per the configuration, the last electron belongs to the s subshell, so it is a part of the s block, and metals always form basic oxide.
Metals react with oxygen to give basic compounds of oxygen. These compounds are usually ionic in nature. Group 1, 2 and lanthanides form basic compounds of oxygen when they react with dioxygen.
Examples: M2O3, MO2, ThO2