Question

write the symbol of each neutral element based on its written electron configuration: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s¹ 1s²2s²2p⁴ 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹

Explanation:

Step1: Count total electrons

For the electron - configuration $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{1}$, sum the exponents: $2 + 2+6 + 2+6 + 2+10 + 6+1=39$. The element with 39 electrons (in a neutral atom, number of electrons = number of protons = atomic number) is Yttrium, symbol Y.

Step2: Count total electrons for the second configuration

For $1s^{2}2s^{2}2p^{4}$, sum the exponents: $2 + 2+4 = 8$. The element with 8 electrons is Oxygen, symbol O.

Step3: Count total electrons for the third configuration

For $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^{10}4p^{6}5s^{2}4d^{10}5p^{6}6s^{2}4f^{1}$, sum the exponents: $2+2 + 6+2+6+2+10+6+2+10+6+2 + 1=57$. The element with 57 electrons is Lanthanum, symbol La.

Answer:

Y
O
La