Question

The table given below shows the mass number and number of neutrons in four elements P,

Q, R and S.

Element P Q R S

Mass number 12 20 23 35

Number of nutrons 6 10 12 18

(i) Which of the following element has atomic number 17?

(a) P (b) Q (c) R (d) S

(ii) P and Q belong to

(a) Group-14 (b) Group-14 and Group-18

(c) Group-1 and Group-17 (d) Group-18 and Group-1

(iii) R and S belong to

(a) Period-2 (b) Period-3 (c) Period-4 (d) Period-5

(iv) Which of the following is a noble gas?

(a) P (b) Q (c) R (d) None of these

(v) Which of the following is an alkali metal?

(a) P (b) Q (c) R (d) S
​

Answer 1

Answer:

i) d

ii) b

iii) b

iv) b

Explanation:

no. of neutrons = mass no.- atomic no.

       atomic no.= mass no. - no of neutrons

for P       = 12-6= 6 Carbon atom 14th group 2nd period

for Q  = 20-10= 10 Neon gas 18th gp and 2nd period

for R   = 23-12 =11 Na atom 1st gp and 3rd period

for S   = 35-18=17 Cl gas 17th gp and 3rd period