An element ‘X’ has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of ‘X’. Also write group number, period number and valency of ‘X’.

Q: An element ‘X’ has mass number 35 and number of neutrons 18. Write atomic number and electronic configuration of ‘X’. Also write group number, period number and valency of ‘X’.

For the given element 'X': - **Atomic Number:** $17$ - **Electronic Configuration:** $2, 8, 7$ - **Group Number:** $17$ - **Period Number:** $3$ - **Valency:** $1$

Metals and Non-metals

Atomic Structure and Periodic Position

Official Answer

For the given element 'X':

Atomic Number: $17$
Electronic Configuration: $2, 8, 7$
Group Number: $17$
Period Number: $3$
Valency: $1$

Atomic number 172, 8, 7Group 17Period 3Valency 1

Marking Scheme

1Calculate atomic number as 17 and write electronic configuration as $2, 8, 7$ (1 mark)
2Identify group number as 17 and period number as 3 (1 mark)
3Calculate valency as 1 (1 mark)

Hint

Use the formula: $\text{Atomic Number} = \text{Mass Number} - \text{Neutrons}$ . Then distribute the electrons into K, L, and M shells.

Quick Oral Answer

The element is Chlorine. Its atomic number is 17, electronic configuration is 2, 8, 7, and it belongs to Group 17, Period 3 with a valency of 1.

Analysis & Explanation

This question tests basic atomic structure calculations and links them to the position of elements in the Modern Periodic Table. The element identified is Chlorine ( $Cl$ ), a highly reactive non-metal that forms ionic compounds with metals like sodium ( $NaCl$ ).

Common Mistakes

1Confusing mass number with atomic number when writing the electronic configuration.
2Writing the group number as 7 instead of 17.

Interesting Facts

Chlorine is a highly reactive, greenish-yellow gas at room temperature and was used as a chemical weapon during World War I due to its toxic nature.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2016?

This question carries 3 marks in the CBSE Class 10 Science 2016 examination.

Which chapter does this question come from in Science?

This question is from the chapter "Metals and Non-metals" in the CBSE Class 10 Science syllabus.

What topic does this question cover in Science?

This question covers the topic "Atomic Structure and Periodic Position" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2016 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2016 paper.