Percentage of gold in $14$ carat gold is (in $\%$)

Which of the following is basic in nature?

The half-lives of two radioactive nuclides $A$ and $B$ are $1 \ min$ and $2 \ min$ respectively. Equal weights of $A$ and $B$ are taken separately and allowed to disintegrate for $4 \ min$. What will be the ratio of weights of $A$ and $B$ disintegrated?

The output characteristics of an $n-p-n$ transistor represent,($I_C=$ collector current,$V_{C E}=$ potential difference between collector and emitter,$I_B=$ base current,$V_{B B}=$ voltage given to base,$V_{B E}=$ the potential difference between base and emitter)

If $(a \times b)^2 + (a \cdot b)^2 = 144$ and $|a| = 4$,then $|b| = $

If the decimal $0.d25d25d25\ldots$ is expressible in the form $n/27$,then $d+n$ must be