(A) Information about atom of some elements. | Element | Atomic number | No. of elements | No. of neutrons | No. of protons | Mass number | |---|---|---|---|---|---| | P | 7 | | | 7 | | | Q | 12 | | | | | | R | 13 | | | | | | S | 13 | | | | 27 | | T | | 15 | | | 30 | | U | | 18 | | 18 | | (i) Find and write values suitable for the places a, b, c, d, e, f. (ii) What is the element that belongs to group V in 3rd period? (iii) Name 2 isotopes among above elements. (iv) (a) Name the element with the lowest reactivity. (b) What is the reason for the lowest reactivity of that element? (B) Elements react with some other elements under various conditions. Among above elements: (a) Name the element that produces oxide and releases hydrogen gas by reacting with steam. (b) Sometimes after adding this element into hot water with a small amount of phenolphthalein, colourless water turns pink. (i) What is the element added to water? (ii) State whether that element is a metal or non-metal?
Answer (1)
(i) Let's fill in the table using the given information:
Element P: Given the atomic number is 7 and the number of protons is also 7, which is consistent (since protons define the atomic number). Neutrons = Mass number - Protons = a - 7. We know Element P is Nitrogen (atomic number 7).
Element Q: The atomic number is 12, which makes it Magnesium. Protons = 12 and if we assume a typical isotope, say 24 for magnesium, then Neutrons = 24 - 12 = 12.
Element R: The atomic number is 13, making it Aluminum. Its typical isotope would have a mass number of 27, so Neutrons = 27 - 13 = 14.
Element S: Its atomic number is 13 and mass number is 27, again confirming that it is Aluminum, similar to Element R.
Element T: We're given the number of elements as 15, with a mass number of 30, which could refer to Phosphorus (atomic number 15), so protons = 15 and neutrons = 30 - 15 = 15.
Element U: The atomic number is 18 and the neutron count is 18, making it Argon (since Protons = 18 for Argon), which is a noble gas. A typical isotope would have the mass number of 36 (18 protons + 18 neutrons).
(ii) The element that belongs to group V in the 3rd period is Phosphorus (Element T).
(iii) Two isotopes among the elements are Aluminum-27 and Aluminum-28, represented by Elements R and S.
(iv) (a) The element with the lowest reactivity in the list is Argon (Element U).
(b) The reason for the lowest reactivity of Argon is that it is a noble gas with a complete outer electron shell, making it chemically stable and inert.
(B) (a) Magnesium (Element Q) reacts with steam to produce magnesium oxide and release hydrogen gas.
(b) (i) The element added to water is Magnesium (Element Q).
(ii) Magnesium is a metal.
