Which atom has two unpaired electrons in the outer valence shell?
O helium
hydrogen
Oxygen
Olithium

Oxygen

Explanation:

The electrons present in an atom are arranged in shells or orbitals. The electrons are filled into these shells based on their energy levels with those shells closest to the nucleus filled first as they have the lowest energies.

The arrangement of electrons around the nucleus of an atom is known as electronic configuration. The outermost electron shell of an atom is known as a valence shell shell and the electrons found in this shell are known as valence electrons. The electrons usually exist in pairs. The first shell can only contain two electrons; the second shell can contain 8. the electrons are singly filled first before pairing occurs.

The electronic configuration of the atoms of the elements in the option are as follows:

Helium : 1s² ; valence electrons are 2 which are both paired

Hydrogen: 1s¹ ; valence electron is 1

Oxygen : 1s²2s²2p⁴ ; valence electrons are 6 wit two unpaired electrons

Lithium : 1s²2s¹ ; valence electron is 1

Helium has two valence electrons but they are paired as its 1s shell can only contain a maximum of two electrons.

Oxygen has 6 valence electrons. Two of these electrons are paired while the other two are unpaired.

explanation:

kim antonie lode clijsters[1] (dutch pronunciation: [kɪm ˈklɛistərs] (about this soundlisten); born 8 june 1983) is a belgian former professional tennis player. clijsters was a world no. 1 in both singles and doubles, having held both rankings simultaneously in 2003. she won a total of six grand slam tournament titles, four in singles and two in doubles.

clijsters competed professionally from 1997 to 2012 in an era where her primary rivals were compatriot justine henin and 23-time grand slam singles champion serena williams. coming from a country with limited success in men's or women's tennis, clijsters became the first belgian player to attain the no. 1 ranking. together with henin, she established belgium as a leading force in women's tennis as the two of them led their country to their first fed cup crown in 2001 and were the top two players in the world in late 2003. individually, clijsters won 41 singles titles and 11 doubles titles on the women's tennis association (wta) tour. she was a three-time winner of the wta tour championships. between singles and doubles, she was a champion at all four grand slam tournaments, winning the us open and the australian open in singles and wimbledon and the french open in doubles with ai sugiyama. her success at majors was highlighted by winning three consecutive appearances at the us open.

plagued by injuries and having lost some of her desire to compete, clijsters initially retired from tennis in 2007 at the age of 23 to get married and have a daughter. she returned to the sport two years later and won her second us open title as an unranked player in just her third tournament back. she defended her title the following year and then won the australian open in 2011 en route to becoming the first mother to be ranked no. 1 by the wta. along with margaret court, she also holds the record for most grand slam singles titles won as a mother with three and was the first to win one since evonne goolagong cawley in 1980. she officially retired from professional tennis after the 2012 us open.

clijsters was born to athletic parents with backgrounds in professional football and gymnastics. she was renowned for her athleticism, which was highlighted by her ability to perform splits on court in the middle of points. she built the offensive side of her game around controlled aggression while also using her exceptional movement to become an elite defensive player. clijsters was very popular and well-liked as a player, having won the karen krantzcke sportsmanship award eight times. she was inducted into the international tennis hall of fame in 2017.

contents

1 early life and background

2 junior career

3 professional career

3.1 1997–99: maiden wta title, newcomer of the year

3.2 2000–02: french open finalist, tour champion

3.3 2003: world no. 1 in singles and doubles

3.3.1 singles: two grand slam finals, tour championship defense

3.3.2 doubles: french open and wimbledon titles

3.4 2004–05: extended injury absence, first grand slam singles title

3.5 2006–07: return to no. 1, hastened retirement

3.6 two-year hiatus

3.7 2009–10: start of second career, back-to-back us open titles

3.8 2011–12: australian open champion, last reign at no. 1

4 national representation

4.1 fed cup

4.2 hopman cup

4.3 olympics

5 rivalries

5.1 clijsters vs. henin

5.2 clijsters vs. williams sisters

5.3 other rivals

6 exhibition matches

7 legacy

8 playing style

9 coaches

10 endorsements

11 personal life

12 career statistics

12.1 performance timelines

12.1.1 singles

12.1.2 doubles

12.2 grand slam tournament finals

12.2.1 singles: 8 (4 titles, 4 runner-ups)

12.2.2 doubles: 3 (2 titles, 1 runner-up)

12.2.3 mixed doubles: 1 (1 runner-up)

13 awards

14 see also

15 references

15.1 books

16 external links

the correct answer is c   with the systems