Write the coefficient of $x^{2}$ in the following polynomial:
$4+7x+3x^{2}$

Evaluate $(421)^{2}$.

Evaluate the following using suitable identities:
$(107)^{2}$

Write the degree of the following polynomial: $ax^3 + bx^2 + cx + d$.

Factorise: $a^{3} - 2\sqrt{2}b^{3}$

Which of the following expressions are polynomials in one variable and which are not? State reason for your answer. If the given expression is a polynomial,state whether it is a polynomial in one variable or not: $x^{2}+2xy+y^{2}$