The elements A, B, C and D have atomic numbers 4, 12, 17 and 19 respectively. Which pair of elements belong to the same period? |
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(a) |
B and C |
(b) |
A and B |
(c) |
A and D |
(d) |
C and D |

The elements A, B, C and D have atomic numbers 4, 12, 17 and 19 respectively. Which pair of elements belong to the same period? |
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(a) |
B and C |
(b) |
A and B |
(c) |
A and D |
(d) |
C and D |

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