Which of the following is not a possible sublevel?
1s
2d
3p
4f

The sub-level that is not possible is 2d.

The values of the subsidiary quantum number (l) must range from 0 to (n - 1). This means that sub - levels in which n = l are not allowed

Recall that s p d f corresponds to 0 1 2 3. So the d orbital has l =2.

Having a 2d  sub - level implies a violation of the rule because n = l which is not allowed.

As a result of this, the 2d sub - level does not exist.

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2d

Explanation:

That is supposed to be 3d. According to the Periodic Table of Elements there are four blocks:

- s block: Alkali Metals and Alkaline Earth Metals [Groups 1 and 2]

- p block: Groups 13 to 18 [including Halogens in Group 17 and Noble Gasses in Group 18]

- d block: Transition Metals, NOT INCLUDING the Actinide and Lanthanide Series [Lanthanide → Atomic Number 57 (Lanthanum) to 70 (Ytterbium); Actinide → Atomic Number 89 (Actinium) to 102 (Nobelium)]

- f block: Actinide and Lanthanide Series [located towards the very bottom of the table to keep the table from being so wide]

** - g block: Hypothetical block of elements, whose outermost electrons are posited to have one or more g-orbital electrons, but no p, d, or f-orbital electrons.

I hope this helps you out alot, and as always, I am joyous to assist anyone at any time.

a. hope i'm right

explanation:

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.