Water is the answer hope this helps
Answer:
Date Significance Soviet Union Mission
August 21, 1957 First intercontinental ballistic missile (ICBM) R-7 Semyorka
October 4, 1957 First artificial satellite First signals from space Sputnik 1
November 3, 1957 First dog in orbit (Laika) Sputnik 2
January 31, 1958 First US satellite, detection of Van Allen radiation belts
Explanation:
ANSWER
2 valence electrons
STEP-BY-STEP EXPLANATION:
The electronic configuration is given below as

Looking at the configuration, you will see that the last energy carries 2 electrons
Hence, the valence electrons are 2