Which of the following equations is true:
(A) $2x + x = 5x$
(B) $2x + 3x = 5x$
(C) $2x + 3x = 5{x^2}$
(D) None of the above

Hint: Here we have to find in which option the right hand side is equal to the left hand side. To find this, we have to find the constant value on both sides and also the degree of the variable on both sides. Here we also have to do some simplification like addition.

Complete step by step answer:
In the above question, we have to find in which option the right hand side is equal to the left hand side.
So, here we will take all the options one by one and choose the correct option among them.
In option (A)
We have,
$2x + x = 5x$
Now, on simplification we get
$3x \ne 5x$
Here we have $3x$ on the left hand side and $5x$ on the right hand side. The coefficient of x is not the same on both sides. So, the above equation is wrong.
Therefore, option (A) is wrong.
In option (B)
We have,
$2x + 3x = 5x$
Now, on simplification we get
$5x = 5x$
Here we have $5x$ on the left hand side and $5x$ on the right hand side. The coefficient of x is the same on both sides. So, the above equation is correct.
Therefore, option (B) is correct.
In option (C)
We have,
$2x + 3x = 5{x^2}$
Now, on simplification we get
$5x \ne 5{x^2}$
Here we have $5x$ on the left hand side and $5{x^2}$ on the right hand side. The degree of x is not the same on both sides. So, the above equation is wrong.
Therefore, option (C) is wrong.

Hence, the correct option is (B).

Note:
We can’t do the above question by putting the particular value of x in the equation and then checking the value on both sides. As we can see, the option (C) is wrong but if we put the value of $x$ equals to $1$, then we get the same value on both sides.