In an electron dot diagram, the symbol for an element is used to represent a. the nucleus. b. the nucleus and all electrons. c. the nucleus and valence electrons. d. the nucleus and all non-valence electrons.

Answer : The correct option is, (A) the nucleus.

Explanation:

Lewis-dot structure : It shows the bonding between the atoms of a molecule and it also shows the unpaired electrons present in the molecule.

In the Lewis-dot structure the valance electrons are shown by 'dot'.

The representation of valence electrons of an atom by dots around the symbol of an element is said to be the electron dot symbol.

In an electron dot diagram, the symbol for an element is used to represent the nucleus.

For example :

As we know that arsenic has '5' valence electrons. So, the symbol (As) is used to represent the nucleus and valance electrons around the is represented by the 'dot'.

The Lewis-dot structure of As (arsenic) is shown below.

the minimum constant speed at which she can catch the train is 2.7 m/s

given:

acceleration = 0.6

time = 4.5 s

to find:

velocity = ?

formula used:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

solution:

from 1st kinematic equation we get,

v = u + at

u = initial speed of train = 0 m/s

v = final speed of the train

a = acceleration of the train

t = time

v = 0 + (0.6 × 4.5)

v = 2.7 m/s

the minimum constant speed at which she can catch the train is 2.7 m/s

answer: 2×10^-2kg

explanation: density= mass per volume

vol=mass/density

converting to s.i units we have;

3÷1000kg = 0.003

1.5÷100m = 0.15

0.003/0.15 = 0.02kg