National and Regional Contests USA Contests USA Physics and Chemistry Contests National Chemistry Olympiad 2010 National Chemistry Olympiad 9 2010 USNCO Local #9: Number of Neutrons Problem Statement How many neutrons are in 0.025 0.025 0.025 24 54 Cr { }_{24}^{54}\text{Cr} 24 54 Cr < s p a n c l a s s = ′ l a t e x − b o l d ′ > ( A ) < / s p a n > 1.5 × 1 0 22 < s p a n c l a s s = ′ l a t e x − b o l d ′ > ( B ) < / s p a n > 3.6 × 1 0 23 < s p a n c l a s s = ′ l a t e x − b o l d ′ > ( C ) < / s p a n > 4.5 × 1 0 23 < s p a n c l a s s = ′ l a t e x − b o l d ′ > ( D ) < / s p a n > 8.1 × 1 0 23 <span class='latex-bold'>(A)</span>\hspace{.05in}1.5\times10^{22} \qquad<span class='latex-bold'>(B)</span>\hspace{.05in}3.6\times10^{23} \qquad<span class='latex-bold'>(C)</span>\hspace{.05in}4.5\times10^{23} \qquad<span class='latex-bold'>(D)</span>\hspace{.05in}8.1\times10^{23} \qquad < s p an c l a ss = ′ l a t e x − b o l d ′ > ( A ) < / s p an > 1.5 × 1 0 22 < s p an c l a ss = ′ l a t e x − b o l d ′ > ( B ) < / s p an > 3.6 × 1 0 23 < s p an c l a ss = ′ l a t e x − b o l d ′ > ( C ) < / s p an > 4.5 × 1 0 23 < s p an c l a ss = ′ l a t e x − b o l d ′ > ( D ) < / s p an > 8.1 × 1 0 23